Inkjet recording method and inkjet recording apparatus

ABSTRACT

An inkjet recording method includes: forming a color image with color inks by while scanning a recording head multiple times on a same recording area, forming a thinned-out image, the recording head having a plurality of nozzle sections for jetting the color inks, wherein a nozzle pitch is from 10 to 50 μm, the color inks comprise C, M, Y and BK inks and at least one special color ink, the color inks contain pigments, at least one organic solvent with high boiling point and water, a dot formed by the color inks has a size of 10 to 50 μm, the recording medium has a transferred amount at 0.04 seconds of absorption time of 10 ml/m 2  or more, the recording medium comprises a micro-porous layer containing inorganic fine particles and a hydrophilic binder; and a 20-degree specular gloss of the recording medium is 20 to 45%.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a novel inkjet recording method andinkjet recording apparatus.

2. Description of Related Art

An inkjet recording mode is one for recording images and texts by flyingminute droplets of ink to adhere onto a recording medium by variousoperation principles, and has advantages such as relatively high speed,low noise and easiness of multiple coloration. In the above inkjetrecording mode, various improvements have been performed in variousfields such as an ink, inkjet recording medium and inkjet recordingapparatus, and at present, the mode has become rapidly popular forvarious fields such as various printers, facsimiles and computerterminals. In particular, recently high-quality picture technology inthe printer has been improved, and its level has come at a picturequality of photograph.

As the inkjet recording apparatus used in the inkjet recording mode, forenhancing a printing speed, those where multiple ink jet openings(nozzle sections) and ink liquid paths are integrated as a recordinghead where multiple recording elements are integrated/arrayed(hereinafter also referred to as a multihead) are used. Additionally, asthe inkjet recording apparatus for corresponding to coloration, thosewhere multiple recording heads composed of the above configuration arecomprised are frequently used. In that case, it is general that therecording heads which ejaculate inks of respective colors are disposedin parallel with a main scanning direction.

Here, when a color image picture is printed, differently from thosewhere only characters are printed in a black-and-white printer, variousfactors such as color density, gradation and uniformity are important toobtain high-quality pictures. In particular, with respect to theuniformity, slight dispersion of nozzle units which occurs in differenceof multihead fabrication steps influences jetting amounts and jettingdirections of inks at respective nozzles, and becomes a cause whichfinally deteriorates image quality as uneven density of a printed image.Also, speed variation at a main scanning of a carriage where heads areloaded, variation of sub scanning paper feeding amount of the medium,and variation of a distance between a medium surface and a nozzle faceon the medium cause deterioration of the image.

For the above problems, a so-called multi-pass recording method has beenproposed where image deterioration due to the dispersion of respectivenozzles and various variations is reduced by scanning multiple times therecording head having multiple nozzle sections onto the same recordingarea on the inkjet recording medium and forming an image according to acomplementary thinning-out pattern. As a mask used in this case, asdescribed in JP-Tokukaisho-60-107975A, the method of using acomplementary pattern with a constant thinning-out rate of a certainrule is the commonest.

However, as described below, when using such a regular mask, converselyuneven colors, stripe unevenness and white spots sometimes remarkablyappear, and thus, the method of using a mask pattern without regularityhas been proposed as an improving countermeasure of this. By forming animage thinned out of this thinning-out pattern without regularity, it ispossible to prevent the uneven density and uneven colors produced due toa synergistic effect of regularity of the image and regularity of themask, and realize high-quality picture and high speed printing to someextent (for example, refer to JP-Tokukaihei-7-52390A,JP-Tokukai-2002-96461A, and JPTokukai-2002-144552A.).

Whereas, the present applicant has found that when a certain inks and arecording medium is used, and in particular when high-quality printingsuch as silver halide photograph is required, sufficient image qualityis not obtained only by the proposed thinning-out printing method. Thisis illustrated below.

The inks used in the inkjet recoding mode are broadly divided into dyeinks where color materials are dissolved in solvents and dispersion inkswhere color materials, mainly pigments are dispersed in solvents. Thedye dissolves in the solvents and is in a molecular state or a clusterstate, which makes its absorption spectrum sharp, and develops clearcolor with high purity. Additionally, there is no particle pattern dueto particles and no scattered light and reflected light occur, thereforeit is possible to obtain an inkjet image with high translucent feelingand clear color phase. The dye has a property excellent inscratch/abrasion resistance because no color material particle ispresent on the surface of media. The dye, however, has drawbacks of poorlight resistance because dye molecules tend to break by photochemicalreaction. The reduction in dye molecular number directly reflects upon acolor density. It is an actual state that the inkjet recording imageusing the dye inks is the high image quality but the poor imagestability against light, and the technology which is superior to silverhalide photographs in the light of stability has not appeared yet.

As the method for solving this problem, pigment inks where the pigmentswith good light resistance are used as colorants have been used for theintended use where the high light stability is required.

In case of using such a pigment, increase of an ink adhesive amountgenerates aggregation of pigment and causes the problem that a colorimage with high quality and definition cannot be obtained. To solve sucha problem, it is possible to apply a method for forming a color image byusing an ink set in which special colors, such as red and violet, isadded to inks of yellow, magenta, cyan and black (for example, seeJP-Tokukai-2003-266913A).

However, when an inkjet image recording according to the thinning-putpattern without regularity is performed using the pigment inks, a dotposition formed at each scanning has no regularity. Therefore, the casewhere the ink droplets of cyan, magenta, yellow and black are adjacentlyprinted on the inkjet recording medium at the same scanning becomesfrequent. As a result, the respective ink droplets are mixed oneanother, aggregation of pigment particles is caused, and a phenomenoncalled bronzing which is hardly caused in the dye inks occurs. A problemthat the color image cannot be accurately reproduced occurs.

In particular, in order to form the image at high definition like asilver halide photograph, when the inkjet recording medium having amicro-porous layer containing inorganic fine particles with a meanparticle size of 100 nm or less is used, an absorption speed of inks isfast and the aggregation of pigment particles present on the recordingmedium occurs more easily. Besides, it has been found that due to usingthe mask pattern without regularity, a probability that different colordots are adjacently printed becomes high, and the formation of image athigh definition becomes difficult because the pigment particles havingdifferent color tone are mixed on the recording medium.

This is because when using the regular thinning-out pattern, theposition of each ink formed on the recording medium at one scanning canbe finely controlled and mixture of the dots can be effectivelyinhibited whereas it is difficult to perform such a control in the casewithout regularity. When a printing rate per scanning by thethinning-out is low, even if using the mask without regularity, theprobability that the dots adjacently formed on the recording mediumbecomes low, and thus, the problem in image quality is reduced.

SUMMARY OF THE INVENTION

The present invention has been made in the light of the above problems.

The above object of the invention is accomplished by the followingconfigurations.

In accordance with the first aspect of the present invention, sn inkjetrecording method comprising the step of: forming a color image withcolor inks on the recording medium by while scanning a recording headmultiple times on a same recording area of the recording medium, forminga thinned-out image according to an thinning-out pattern withoutregularity in each scanning, the recording head having a plurality ofnozzle sections for jetting the color inks, wherein a nozzle pitch ofthe recording head is from 10 to 50 μm, the color inks comprise cyan,magenta, yellow and black inks and at least one special color ink, thecolor inks contain pigments, at least one organic solvent with highboiling point and water, a dot formed by jetting the color inks from therecording head has a size of 10 to 50 μm on the recording medium, therecording medium has a transferred amount at 0.04 seconds of absorptiontime by Bristow method of 10 ml/m² or more, the recording mediumcomprises a micro-porous layer containing inorganic fine particleshaving a mean particle size of 15 to 100 nm and a hydrophilic binder;and a 20-degree specular gloss of the recording medium according toJIS-Z-8741 is 20 to 45%.

In accordance with the second aspect of the present invention, an inkjetrecording apparatus for forming a color image by jetting color inks on arecording medium, comprising: a recording head having a plurality ofnozzle sections to jet the color inks, the nozzle sections being arrayedat a pitch of 10 to 50 μm; a scanning section to make the recording headscan multiple times on one recording area of the recording medium; and acontrol section to allow the recording head to jet the color inks fromthe plurality of nozzle sections so that a thinned-out image accordingto a thinning-out pattern without regularity in each scanning is formedon the recording medium, wherein the color inks comprise cyan, magenta,yellow and black inks and at least one special color ink, the color inkscontains pigments, at least one organic solvent with high boiling pointand water, a dot formed by jetting the color inks from the recordinghead has a size of 10 to 50 μm on the recording medium, the recordingmedium has a transferred amount at 0.04 seconds of absorption time byBristow method is 10 ml/m² or more, and the recording medium has amicro-porous layer containing inorganic fine particles having a meanparticle size of 15 to 100 nm and a hydrophilic binder, and a 20-degreespecular gloss of the recording medium according to JIS-Z-8741 is 20 to45%.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not intendedas a definition of the limits of the present invention, and wherein:

FIG. 1 is a perspective view representing a major configuration sectionof an inkjet printer;

FIG. 2 is a perspective view where a carriage of the inkjet printer isenlarged;

FIG. 3 is a bottom view of recording heads of the inkjet printer;

FIG. 4 is a block diagram representing a control section of the inkjetprinter;

FIG. 5 is a block diagram representing a configuration of an imageforming apparatus;

FIGS. 6A to 6C are schematic diagrams representing one example ofmulti-pass printing inkjet recording methods;

FIGS. 7A to 7C are schematic diagrams representing one example ofmulti-pass printing inkjet recording methods;

FIGS. 8A to 8C are schematic diagrams representing one example ofmulti-pass printing inkjet recording methods;

FIGS. 9A to 9C are schematic diagrams representing one example ofmulti-pass printing inkjet recording methods;

FIG. 10 is a schematic diagram representing one example of imagealignment patterns arrayed regularly;

FIG. 11 is a schematic diagram representing another example of imagealignment patterns arrayed regularly;

FIG. 12 is a schematic diagram showing a printing condition when arrayedimage data in an increased duty were input;

FIGS. 13A and 13B are schematic diagrams showing a condition where headsjet ink droplets on a flat face of the recording medium at a constantspeed v with moving at a constant speed V in a forth or back direction;

FIG. 14 is a schematic diagram showing a jetted dot condition when animage with 100% duty was bidirectionally printed using staggeredthinning-out masks;

FIG. 15 is a schematic diagram showing one example of methods ofperforming multi-pass recording using masks without regularity;

FIG. 16 is a schematic diagram showing another example of methods ofperforming multi-pass recording using masks without regularity;

FIG. 17 is a schematic diagram showing one examples of nozzle alignmentscorresponding to mask patterns;

FIG. 18 is a schematic diagram showing one example of mask patterns withblue noise property;

FIG. 19 is a schematic diagram showing one example of mask patterns;

FIG. 20 is a schematic diagram showing another example of mask patterns;

FIG. 21 is a schematic diagram showing another example of mask patterns;

FIG. 22 is a block diagram showing one example of mask processingcircuits;

FIG. 23 is a schematic diagram showing one example of mask patterns usedin Comparative Examples; and

FIG. 24 is a graph showing an example of relationship between image dataand the ink amount to be used.

PREFERRED EMBODIMENTS OF THE INVENTION

Hereinafter, the best modes for carrying out the invention areillustrated in detail, but the invention is not limited thereto.

First, a inkjet printer to which the inkjet recording method of theinvention can be applied is illustrated in reference to FIG. 1. FIG. 1is a perspective view representing a major configuration of the inkjetprinter.

As is shown in the figure, an image forming section 2 where inks arejetted onto a recording medium to form an image is installed in theinkjet printer 1. In this image forming section 2, a platen 21 whichsupports a back face (face opposite to a side of a recorded face) of arecording medium in a given range by its upper face is nearlyhorizontally arranged. A guiding member 25 which extends along ascanning direction X over the platen 21, for moving a carriage asscanning member 23 which scans in the scanning direction X is installedin the image forming section 2.

In the carriage 23, recording head 22 which jet the inks on therecording medium and a linear encoder sensor 27 which reads an opticalpattern of a linear scale 26 where the optical pattern extends along thescanning direction X and is arranged in its longitudinal direction with300 dpi cycle to output as clock signals are loaded. Meanwhile, dpireferred to in the invention represents a dot number per 2.54 cm. In thepresent embodiment, printing operation is performed by dividing thisencoder signal, for example, by a printing resolution of 1200 dpi. Amoving direction of the carriage 23 is changed by a rotation directionof a driving motor for the carriage, and the carriage 23 is moved backand forth in the scanning direction X by this. At the image formation,the carriage 23 moves forth, back or back and forth when the recordingmedium stops. A moving speed at that time is, for example, 705 mm/sec atthe highest speed.

Next, the recording heads 22 are illustrated in reference to FIG. 2 andFIG. 3. FIG. 2 is a perspective view of the enlarged carriage 23, andFIG. 3 is a bottom view of the recording head 22.

The recording head 22 may be a piezo mode or a thermal mode, but ispreferably the thermal mode in terms of arranging the nozzles at highdensity, and the recording heads of thermal mode are used in the presentembodiment. This recording head 22 is arranged such that a recordingface of the recording medium fed on the platen 21 is faced to a nozzleface 222 at the image recording where the nozzles 221 of the recordingheads 22 are formed.

As shown in FIG. 2, total 256 nozzles at a pitch of 42.3 μm (600 dpi)with two rows of each 128 are formed in a feeding direction of therecording medium on the nozzle face 222 of the recording heads. Thesenozzle rows are arranged with 21.2 μm out of alignment one another. Thiscorresponds to one pixel in 1200 dpi. A distance between two rows isabout 500 μm. A thermal inkjet element is installed inside each nozzle221, and the ink as a droplet is separately jetted by operation of ajetting member.

The ink is supplied to each recording head passing through a tube forpiping from a cartridge for recording ink which is not shown in thefigure. Four recording heads 22 are disposed side by side along thescanning direction, and are used for 4 color inks of cyan (C), magenta(M), yellow (Y) and black (K) and 3 special color inks, andrespectively. In the present Examples, 7 type inks of C, M, Y and K and3 special colors are used as the recording inks, but the effects of theinvention are the same even in the inkjet printer which records 9 colorsor more, for example, 8 colors of dark and light C, M, Y and K usinglight colors and 3 special colors. In FIG. 1, the recording heads for 11colors are loaded, but the printing is performed using 7 of them in thepresent Examples.

Next, a control section of the inkjet printer 1 is illustrated inreference to FIG. 4. FIG. 4 is a block diagram representing the controlsection of the inkjet printer 1.

As shown in FIG. 4, the control section 100 is configured by connectinga feeding motor 101 to feed the recording medium, CPU 103, an interface104, a driving motor 231 for the carriage, a memory write controller105, an image memory 106, a memory read controller 107, and a maskprocessing circuit 108 through a bus 110 as is shown. A detailedconfiguration of the mask processing circuit 108 is described below. Therecording head 22 of the inkjet printer 1, respective driving sectionsand the like are also connected to the control section 100.

The control section 100 controls feeding of the recording medium,scanning of the carriage 23 and ink jetting of the recording head 22,and the like. As is shown in FIG. 4 and FIG. 5, an image formingapparatus 200 such as computer is connected. The image forming apparatus200 forms an image with multiple colors based on input signals. In thisinstance, an application program 201 which operates inside the imageforming apparatus 200 displays the image on a monitor 300 through avideo driver 202 with processing the image. When this applicationprogram 201 puts an image formation direction in motion, the printerdriver 203 of the image forming apparatus 200 receives image data forthe image formation from the application program 201, and the image dataare converted into signals capable of forming the image in the inkjetprinter 1.

The printer driver 203 comprises a rasterizer 204 which converts theimage data dealt in the application program 201 into image gradationdata including color information of dot units, a color gradationcompensation module 205 which compensates the image gradation data inaccordance with color density property and gradation property of theinkjet printer 1, and a halftone module 206 which produces the imagedata of so-called halftone where a density at a certain area isexpressed by the presence or absence of the recording inks at dot unitsfrom the image data after the color compensation. A module 207 whichperforms the thinning-out mask processing can be also incorporated inthis printer driver. In that case, a mask setting can be changeddepending on a type of the recording medium used for the printing, andthus more flexible control is possible than the processing in theprinter. When the mask processing circuit 108 is used, the processing atthe module 207 is not performed. Conversely, when the mask processing isperformed at the module 207, the processing at the mask processingcircuit 108 the is not performed. Also, it is possible to download amask pattern every printing from the image forming apparatus 200.

Next, multi-pass inkjet recording method is illustrated. As mentionedabove, in the inkjet image recording, particularly when a color imagepicture is formed, various factors such as color density, gradation anduniformity are required. In particular, with respect to the uniformity,slight unevenness of nozzle units which occurs in difference atmultihead fabricating influences jetting amounts and jetting directionsof inks at respective nozzles, or strip-shaped unevenness occurs due tomechanical accuracy at movement of the recording medium, and as aresult, becomes a cause which finally deteriorates image quality asuneven density of a printed image. Thus, in the present embodiment, tosolve such problems, the color image is formed using the multi-passinkjet recording method where the recording heads 22 are scannedmultiple times onto the same recording area of the inkjet recordingmedium.

As the multi-pass ink jet recording method, it is possible to use themethod, for example, in JP-Tokukaisho-60-107975A. That method isillustrated by FIGS. 6A, 6B and 6C, and FIGS. 7A, 7B, and 7C.

This method shows the multihead 1101 is scanned three times to completea printing area shown in FIGS. 8A, 8B and 8C, and FIGS. 9A, 9B and 9Cand a half thereof, 4 pixel unit area is completed by scanning twotimes. In this case, 8 nozzles of the multihead are divided into upper 4nozzles and lower 4 nozzles, and dots printed by scanning one nozzleonce are those where defined image data are thinned-out to about a halfaccording to given image data alignment. And at the second scanning,dots are filled in the image data of a remaining half to complete theprinting in the 4 pixel unit area.

When using such a recording method, even if using the same one as themultihead shown in FIGS. 9A, 9B and 9C influences intrinsic for eachnozzle on a printing image are reduced by half, and therefore, theprinted image becomes like FIG. 6B, and black lines and white linesobserved in FIG. 9B become indistinctive. Therefore, uneven density asshown in FIG. 6C is considerably alleviated compared to the case of FIG.9C.

When such recording is performed, the image data are divided to offsetone another of the certain alignment in the first scanning and thesecond scanning. Typically, as shown in FIGS. 7A, 7B and 7C it is thecommonest to use one like staggered grids every vertical and horizontalone pixel as this image data alignment (thinning-out pattern).

Accordingly, in a unit printing area (here 4 pixel unit), the printingis completed by the first scanning where staggered grids are printed andthe second scanning where inverse staggered grids are printed.

FIGS. 7A, 7B and 7C illustrate how the record in the given area iscompleted when these staggered and inverse staggered patterns are used,respectively using the multihead with 8 nozzles as with FIGS. 6A, 6B and6C. First, in the first scanning, the recording of the staggered pattern(shaded circles) is performed using the lower nozzles (FIG. 7A). Next,in the second scanning, paper feeding is performed for 4 pixels (a halfof a recording head length) and the recording of the inverse staggeredpattern (white circles) is performed (FIG. 7B). Further, in the thirdscanning, the paper feeding is performed again for 4 pixels (a half of arecording head length) and the recording of the staggered pattern isperformed (FIG. 7C).

This way, the recording area of 4 pixel unit every one scanning iscompleted by alternately performing the paper feeding of 4 pixel unitand the recording of the staggered or inverse staggered pattern insequence. As illustrated above, it is possible to obtain high-qualityimage which uneven density is alleviated by completing the printing bythe different two types of nozzles in the same area.

However, even when such multi-pass recording is performed, the aboveuneven density is not sometimes dissolved at all and new uneven densityis sometimes affirmed particularly in halftone depending on duties. Suchphenomena are illustrated below.

Typically, the image data to be recorded in a certain area, which theprinter receives, have been already arrayed regularly. In the side ofthe recording apparatus, a definite amount of those data is stocked inbuffer, new mask (image alignment pattern) of the staggered or inversestaggered pattern is given as is already illustrated, and the printingof that pixels is performed only when both the image data and pattern ofthe mask become an ON state.

FIGS. 10 to 12 illustrate these appearances. In FIG. 10, 1710 representsalready arrayed data stocked in the buffer, 1720 represents thestaggered pattern mask indicating pixels which allow the printing in thefirst scanning, 1730 represents the inverse staggered pattern maskindicating pixels which allow the printing in the second scanning, 1740and 1750 represent the pixels printed in the first scanning and thesecond scanning, respectively.

In FIG. 10, the already arrayed data in the case where 25% printing isperformed in a certain area are stocked in the buffer. These datauniformly retain the density in an assigned definite area, and thus, itis common that the printing data are disposed in a scattered state aspossible. What image alignment these are is dependent on how areagradation method is performed at image processing before beingtransferred to the printer body. Those shown in 1710 are one instance ofthe image alignment for 25% data. When masks of 1720 and 1730 are givento such data and the printing is performed, as shown in 1740 and 1750,the data are allocated and recorded in a state where the data aredivided equally in the first scanning and the second scanning,respectively.

However, as is shown in FIG. 11, when just 50% data come, it can beeasily supposed that the data 1810 of image alignment in the mostscattered state are completely coincided with either the staggeredpattern mask (1820) or the inverse staggered pattern mask (1830).

When such a phenomenon occurs, the printing of all image data isterminated in the first scanning (1840) and the recording is notperformed in the second scanning (1850) at all. Thus, all printing dataare printed by the same nozzles. Therefore, the influences of nozzledispersion are directly reflected upon the uneven density, and originalpurposes of the above division recording method are not accomplished.

FIG. 12 exhibits a printing state when arrayed image data at a higherduty state than FIGS. 10 and 11 are input. Also in this, it is foundthat the number of printing dots is considerably different in the firstscanning and the second scanning. This way, there has been an adverseeffect that the uneven density which has been improved at high duty ofaround 100% appears again for the data at low to around 50% duty.

When the thinning-out printing is performed using a specified maskpattern, the printing data and the mask pattern have sometimes the samecycle. An amplitude due to an allocation of the printing pixels andnon-printing pixels on the mask pattern and an amplitude of the printingdata are overlapped and vibrate sympathetically. Dot alignments of theimage formed by this has a pattern with a certain orientation.Typically, this phenomenon is called a moire. This is easily remarkableand easily recognized by users when the images using the same maskpattern are in multiple lines. This moire heavily depends on periodicityof the mask pattern.

In addition to the above problems, the following problems occur whenbidirectional printing is performed.

FIG. 13A exhibits a state where as the recording head jets a ink dropleton a smooth face of the recording medium at a constant speed v withmoving in a forth or back direction at a constant speed V. If the faceof the recording medium is smooth as in the figure and a distance dbetween the face of the recording medium and a nozzle face of therecording head is constantly retained at a constant value, a dot printedin a forth route and a dot printed in a back route are formed on thesame position by primarily adjusting a jet timing in the forth and backroutes. However, when the face of the recording medium itself is liftedabove an actual position as shown in FIG. 13B for some reason, thedistance between the nozzle face and the face of the recording medium isshortened to d′, and a time from jetting by the recording head toarrival of the ink droplet onto the face of the recording medium isshortened in both forth and back routes. Therefore, printed dots areformed on the positions out of the aimed position as shown in a lowerfigure. Likewise, when on the same image area, the distance d betweenthe face of the recording medium and the nozzle face at printing in theforth route and the distance d between the face of the recording mediumand the nozzle face at printing in the back route are changed due tolocal lifting of the paper, formed positions are sometimes furtherseparated.

In such a state, when the image at duty of 100% is bidirectionallyprinted using the staggered thinning-out mask, a jetted dot statebecomes one like FIG. 14. Here, the state where each dot is ¼ pixel outof a proper position is shown. Portions where adjacent dots areoverlapped more than needs and portions where spaces between adjacentdots are excessively large appear in different allocations depending onthe thinning-out mask. In FIG. 14, all dots are printed in an inversedirection of adjacent dots, and thus a space of one dot every one dotoccurs and the state where the print density is entirely light occurs.

Such total displacement of jetted positions at the bidirectionalprinting occurs not only due to partial lows and highs of the face ofthe recording medium as shown in FIG. 13 but also due to various causessuch as uneven jetting speed of the recording head 22 and uneven movingspeed of the carriage. It is difficult to control the jet timing at thebidirectional printing because values of these factors are not constantfor a traveling direction of the carriage. Also, the distance betweenthe recording head 22 and the face of the recording medium in therecording apparatus is sometimes much different depending on individualapparatus, and thus control of jetting positions in the forth and backroutes by adjustment of the jet timing has a limitation.

Due to the adverse effects described above, sufficient image quality isnot always obtained with respect to the uneven density in the multi-passrecording using the regular thinning-out pattern which has beenconventionally performed to compensate the variation of nozzles and thelike. These adverse effects for the uneven density has the periodicitywhere unevenness alternately appears at a certain width of printingarea, and thus it facilitates human visual sensation which recognizes asthe uneven density.

The present inventors have found that the above issues occur when theregular mask pattern is used. Thus, in the present embodiment, the aboveproblems are solved by performing the multi-pass recording using athinning-out pattern without regularity, which defines an array ofnon-record pixel locations and record pixel locations, instead of usingthe regular mask pattern. As the thinning-out pattern withoutregularity, for example, it is possible to use a random pattern of agiven size prepared using random numbers. Specifically, for example, asdescribed in JP-3176182B, multiple random mask patterns with a givensize where non-recording pixels and recording pixels are randomlyarrayed are produced, the produced random mask patterns can be used asmasks for thinning out recording data as thinning-out patterns for eachrecording area.

By forming the printed image in accordance with such random maskpatterns, to have pattern cycles on the thinning-out alignment can beinhibited, that is, the adverse effect of uneven density in the formedimage which occurs in the conventional multi-pass recording method usingthe regular masks can be overcome by eliminating the periodicity ofuneven density.

Also, in place of the random mask using such random numbers, a dotallocation pattern with so-called blue noise property may be used as thethinning-out pattern without regularity. This pattern has been developedfor quantization processing of halftone. When a dither processing isperformed using this pattern, there are characteristics that less lowfrequency component is contained in the produced dots and the imagewhere a particle feel is reduced is obtained.

In order to perform the image formation according to the thinning-outpattern without regularity, the method is not limited to the methodusing the random mask using random numbers or the dot allocation patternwith the blue noise property, and the other similar patterns for formingthe thinned-out image of the thinning-out pattern without regularity canbe used.

Next, with respect to the method of performing the multi-pass recordingusing the masks without regularity as the above, the case where 4scanning printing is performed using the dot allocation pattern with theblue noise property as the mask is illustrated below in reference toFIGS. 15 and 16.

In an actual figuration of the nozzles of the recording head 22 used forthe recording, as shown in FIG. 3, nozzle rows of 128 nozzles arrangedat a pitch of 600 dpi are disposed in the main scanning direction at adistance of 500 μm.

Hereinafter, to simplify the illustration of the multi-pass recording,the nozzles were 16 per color, this was divided into 4 to make a nozzlenumber per divided area 4, and a mask size corresponding to it was made4×16. The divided areas corresponding to this are shown as 501 to 504 inFIG. 17. The 4 scanning printing is realized by making use of therespective divided areas 501 to 504 separately.

In each scanning, a thinning-out mask pattern with about 25% duty, thus,the mask pattern where a printing acceptable rate is about 25% is setfor the printing data for each divided area, and a 100% image is made byscanning 4 times. A1 to A4 which are examples of the 4×16 mask patternsused for this are shown in FIG. 15. In each mask pattern A1 to A4, themask data exist at a position on grids shown by a mesh pattern in thefigure, and the mask patterns are configured such that the mask datafill all grids of 4×16 when the respective mask patterns A1 and A4 areoverlaid.

For the printing data 800 (hatching portions indicate that there are theprinting data) shown in FIG. 15, the above mask patterns A1 to A4 areset. Here, a logical add at the same position of the printing data 800and each mask pattern A1 to A4 is taken by making the presence ofprinting data 1 and making the absence of data 0 for the printing data800 and making the presence of mask data 1 and making the absence of thedata 0 for the mask patterns A1 and A4, and jetted data 801 to 804 ofthe recording heads are produced, respectively. When the 4 jetted data801 to 804 are overlaid, the same printed image 805 as the originalprinting data 800 is formed.

FIG. 16 is a view for illustrating the multi-pass printing. Four typesof mask data groups of a group of A1 to A4, a group of B1 to B4, a groupof C1 and C4 and a group of D1 and D4 are used as one cycle of 4 pass.The pattern in each group is the pattern such that a 100% image iscompleted when four are overlaid in any cases. In the multi-passprinting, such setting of the mask data is performed in each dividedarea 501 to 504 of the recording head 22 in each scanning.

Print is performed as follows.

In the first printing area on a print image, the mask pattern A1 is setfor the divided area 504 of the recording head 22 and the recording isperformed in the first scanning. Subsequently, in the second scanning,in the first printing area, the mask pattern A2 is used for the dividedarea 503 of the recording head 22, and in the second printing area, theprint is performed using the mask pattern B1, of which the group isdifferent from that of the mask pattern used in the first printing area,for the divided area 504 of the recording head 22.

Further, in the third scanning, the print is performed using the maskpattern A3 for the divided area 502 of the recording head in the firstprinting area, the mask pattern B2 for the divided area 503 of therecording head in the second printing area, and the mask pattern C1, ofwhich the group is different from those of the mask patterns A3 and B2,for the divided area 504 of the recording head in the third printingarea.

And in the fourth scanning, the print is performed using the maskpattern A4 for the divided area 501 of the recording head in the firstprinting area, the mask pattern B3 for the divided area 502 of therecording head in the second printing area, the mask pattern C2 for thedivided area 503 of the recording head in the third printing area, andthe mask pattern D1, of which the group is different from those of themask patterns A4, B3 and C2, for the divided area 504 of the recordinghead in the fourth printing area. At that time, in the first printingarea, total four times of scanning are performed using 4 mask patterns,A1, A2, A3 and A4, and the image print for this area is completed.

By the same procedure, the image formation is made using mask patternsB1, B2, B3 and B4 in the second printing area, using mask patterns C1,C2, C3 and C4 in the third printing area, and using mask patterns D1,D2, D3 and D4 in the fourth printing area. Subsequently, the printing iscontinued by repeatedly making use of the printing using mask patternsA1, A2, A3 and A4 in the fifth printing area and mask patterns B1, B2,B3 and B4 in the sixth printing area, and the patterns of these 4groups.

Also, as is shown in FIG. 18, these patterns are four mask patterns eachhaving the blue noise property when the patterns are respectivelyaligned from the upper in sequence of A4B3C2D1, B4C3D2A1, C4D3A2B1 andD4A3B2C1 to configure four 16×16 masks. These four 16×16 masks are thosewhere 0 to 255 are disposed on 16×16 grids to have the blue noiseproperty and the portions corresponding to the values of 0 to 63, 64 to127, 128 to 191 and 192 to 255 are used as recording acceptable pixels.Those where these four masks are divided into four 4×16 correspond to A1to A4, B1 to B4, C1 to C4 and D1 to D4. How to make such patterns isdescribed in, for example, JP-2622429B.

This way, when the blue noise property is given to the dot patternitself formed by one scanning, there are effects that occurrence of therepeated pattern and particulate deterioration are reduced compared tothe case using the patterns produced by the random numbers. This isdescribed in, for example, Tokukai2002-96461.

If the acceptable printing rate of the mask is changed, the mask afterchange can be easily obtained by changing the values of these 0 to 255depending on a printing rate. For example if making two pairs of 40% and10% masks, the masks could be made by making the pixels corresponding to0 to 102, 103 to 127, 128 to 230 and 231 to 255 the printing acceptablepixels, respectively. Examples of such masks are shown in FIGS. 19 to21.

FIG. 22 is a block diagram showing a configuration of the maskprocessing circuit, and illustrates the mask processing circuit 108 inFIG. 4 in detail. In FIG. 22, 301 is a data register connected to amemory data bus, for reading out the printing data accumulated in animage memory 106 in a memory and temporarily storing, 302 is aparallel/serial converter for converting the data stored in the dataregister 301 into serial data, 303 is an AND gate for applying the masksto the serial data, and 304 is a counter for managing data transfernumbers.

The reference numeral 305 is a register connected to CPU 103 through CPUdata bus, for storing the mask patterns, 306 is a selector for selectinga digit position of the mask pattern, 307 is a selector for selecting aline position of the mask pattern, and 311 is a counter for managing thedigit position.

In a transfer circuit shown in FIG. 22, a serial transfer of printingdata to the recording head 22 is performed by printing command signalssent from the CPU 103. The printing data accumulated in the image memory106 in the memory are temporarily stored in the data register 301, andconverted into the serial data by the parallel/serial converter 302. Themasks are applied to the converted serial data by the AND gate 303, andsubsequently the data are transferred to the recording head 22 head. Thetransfer counter 304 counts a transfer bit number and transfers the datafor 16 nozzles.

A mask register 305 is configured by four mask registers, A, B, C and D,mask patterns written by the CPU 103 are housed. Each mask registerstores the mask pattern of vertical 16 bits and horizontal 16 bits. Aselector 306 selects mask pattern data corresponding to a digit positionby making a value of a column counter 111 a selection signal. Also, theselector 307 selects mask pattern data corresponding to a line positionby making a value of a transfer counter 304 a selection signal. Themasks are applied to the transfer data using the AND gate 303 by themask pattern data selected by the selectors 306 and 307.

These data are used for injection control of each nozzle of therecording head 22, and an injection is performed by synchronizing withtiming signals produced from encoder signals. Hereinafter, theseoperations are performed in conformity with printing resolution towardto a width direction of the recording medium. In this embodiment, a masksize is 16 in a horizontal direction, and thus, the same mask pattern isrepeatedly used every 16 pixels, but it is also possible to make thesize in the horizontal direction of the mask the same size as the widthof the recording medium. As the present embodiment, it is possible toreduce a capacity of the register which memorizes the masks byrepeatedly using the same mask pattern.

In the inkjet recording method and the inkjet recording apparatus of thepresent embodiment, it is one of characteristics that a nozzle pitch ofthe recording head is from 10 to 50 μm. If the nozzle pitch is 50 μm orless, when jetted ink droplets are printed side by side one another, thedistance between the droplets becomes short, and thus a problem ofbronzing by adjacent dots one another easily occurs. Therefore, effectsby applying the invention to the case that the nozzle pitch is 50 μm orless are great. This reason is that dot sizes on the recording medium isexpanded approximately twice as large as the size of nozzle usedordinarily, and a dot jetted position on the recording medium isdisplaced from the proper position to be jetted at by unevenness ofangles in jetting from the nozzle.

Besides, by making the nozzle pitch short such as 50 μm or less, evenwhen multiple nozzles which exceed 500 nozzles per recording head aremade, it is possible to keep an entire recording head length short. Thiscan suppress jetted ink out of the position on the recording mediumattributed to a change of a flying distance of the ink droplet from thenozzle in a recording head length direction due to a slope between therecording medium surface and the nozzle face, and thus it is possible toretain high printing accuracy. By making the nozzle pitch 10 μm or more,it is possible to suppress disturbance in fabrication aptitude, andconsequently, it is possible to suppress the jetted ink out of theposition, make it suppress to cause an overlap of dots due to shorteningof dot intervals in the recording head length direction, and suppressthe problem such as bronzing.

The nozzle pitch referred to here is a separation distance of mutualnozzles in the nozzle group arranged nearly in a line. As FIG. 3, in thecase where two rows of the nozzle groups are arranged by shifting at ahalf pitch, when adjacent dots in a sub scanning direction on therecording medium are formed by nozzles of an A row and a B row, acertain time difference occurs. When the distance between the A row andthe B row is relatively long, after a dot which previously adheres isabsorbed into the recording medium, then next dot adheres, and thus itis difficult to cause the bronzing due to the aggregation of ink. Thisway, when the distance between the A row and the B row is relativelylong, the nozzle pitch is a pitch in each A row and B row. On the otherhand, when the distance between the A row and the B row is relativelyshort, the nozzle pitch is the distance between adjacent nozzles betweenthe A row and the B row, and typically a half of the pitch in each A rowand B row.

Thus, in the invention, when the distance between the most separatenozzle rows (distance between N1 and Nn, i.e., in the case of threerows, the distance between the first row and the third row) of multiplerows (n rows such as N1, N2 . . . Nn) of the nozzle groups is 4 mm orless, the nozzle pitch is 1/n of the pitch in each row, whereas when thedistance is more than 4 mm, the nozzle pitch is the pitch in each rowbecause it is preferable to consider influences for aggregation.

In the inkjet recording method of the invention, it is preferred that aprinting acceptable rate by the thinning-out pattern is from 15 to 35%.Here, in the invention, the printing acceptable rate is a rate of dotnumber where jetting of the ink is acceptable in one main scanning basedon total dot number in the pattern when using the thinning-out pattern.

When the printing is performed using multiple thinning-out patternsdifferent in printing acceptable rate in one image, the image quality ofthe image after the printing is frequently attributed to thethinning-out pattern with high printing acceptable rate. Therefore, inthe invention, when the multiple thinning-out patterns different inprinting acceptable rate are used in one image, the acceptable rate ofthe thinning-out pattern with the highest printing acceptable rate inthe thinning-out patterns used in one image is the printing acceptablerate.

By making the printing acceptable rate by the thinning-out pattern 15%or more, the probability that the jetted ink droplets are printed sideby side one another becomes high, and therefore the effects obtained byapplying the properties of the inks, the medium and the recording methodof the invention are great. Thus, by applying the invention, thehigh-quality images with less bronzing can be obtained. On the otherhand, by making the printing acceptable rate 35% or less, in theportions where adhering liquid amounts are large such as red, blue anddark grey, the high quality images can be obtained.

It is preferred that a dot size formed by the color ink jetted from therecording head is from 10 to 50 μm on the recording medium. By makingthe dot size formed by the color ink 10 μm or more, it is possible tomaintain a printing efficiency at a certain level or more, andaccurately control an ink droplet size. Also, by making it 50 μm orless, it is possible to suppress the bronzing due to the ink dropletsone another printed side by side, and obtain the images at highdefinition.

In the present invention, at least one special color ink is usedtogether with basic color inks of yellow, magenta, cyan and black. Aspecial color ink is an ink having a color between one color of basiccolors (cyan, magenta and yellow) and another color of the basic colors,and for example, means an ink of red, green, violet, orange, blue or thelike. By using the special color ink together with basic color inks ofyellow, magenta, cyan and black, it is possible to reduce the amount ofinks to be jetted. As a result, it is possible to prevent aggregation ofpigment particles which are comprised in jetted ink and realize a colorimage with high quality and high definition in which decrease of gloss,bronzing, and color turbidity are suppressed.

In case of using such a special color, there are more kinds of ink thanordinary printing with CMYK inks. No method for separating input imagedata (RGB, CMYK or the like) into respective colors is established as acommon belief, and technical know-how depending on inks to be used isrequired. As for this, color separation in accordance with a specialcolor to be used is made possible by using the art enclosed inJP-Tokukai-2000-32284A by the present applicant, or the like. Accordingto this art, it is possible to use the color gamut extended by a specialcolor ink most effectively and also secure continuity of colorcalorimetrically.

In addition to this, alternatively, such a method as described inJP-2711081B can generate special color version of data. According to themethod, data value for a blue ink is generated from data values of cyanand magenta. It is possible to perform ink amount control, such asreducing the total ink amount by cutting down data value for cyan andmagenta depending on the data, and reducing roughness by usinglight-colored cyan and magenta without a special color in highlightpart.

Next, the color inks according to the invention are illustrated.

The color inks of the invention contain pigments, at least one organicsolvent with high boiling point and water, and additionally it ispreferred that a surface tension of the color inks is from 30 to 50 mN/mand the pigments are dispersed by a polymeric dispersant.

As the pigments which can be used for the invention, it is possible touse chromatic organic or chromatic inorganic pigments known in the art.For example, azo pigments such as azo lake, insoluble azo pigments,condensed azo pigments and chelate azo pigments, polycyclic pigmentssuch as phthalocyanine pigments, perylene pigments, anthraquinonepigments, quinacridone pigments, dioxazine pigments, thioindigopigments, isoindolinone pigments and quinophthalone pigments, dye lakessuch as basic dye lake and acid dye lake, organic pigments such as nitropigments, nitroso pigments, aniline black and daylight fluorescentpigments, and inorganic pigments such as carbon black are included butthe invention is not limited thereto.

Specific organic pigments are exemplified below.

As the pigments for magenta, for example, C.I. Pigment Red 2, C.I.Pigment Red 3, C.I. Pigment Red 5, C.I. Pigment Red 6, C.I. Pigment Red7, C.I. Pigment Red 15, C.I. Pigment Red 16, C.I. Pigment Red 48:1, C.I.Pigment Red 53:1, C.I. Pigment Red 57:1, C.I. Pigment Red 122, C.I.Pigment Red 123, C.I. Pigment Red 139, C.I. Pigment Red 144, C.I.Pigment Red 166, C.I. Pigment Red 202, C.I. Pigment Red 222, C.I.Pigment Violet 19 and the like are included.

As the pigments for red, for example, C.I. Pigment Red 17, C.I. PigmentRed 49:2, C.I. Pigment Red 112, C.I. Pigment Red 149, C.I. Pigment Red177, C.I. Pigment Red 178, C.I. Pigment Red 188, C.I. Pigment Red 255,C.I. Pigment Red 264 and the like are included.

As the pigments for yellow, for example, C.I. Pigment Orange 31, C.I.Pigment Yellow 12, C.I. Pigment Yellow 13, C.I. Pigment Yellow 14, C.I.Pigment Yellow 15, C.I. Pigment Yellow 17, C.I. Pigment Yellow 74, C.I.Pigment Yellow 93, C.I. Pigment Yellow 94, C.I. Pigment Yellow 128, C.I.Pigment Yellow 138 and the like are included.

As the pigments for orange, for example, C.I. Pigment Orange 36, C.I.Pigment Orange 43, C.I. Pigment Orange 61 and the like are included.

As the pigments for cyan, for example, C.I. Pigment Blue 15, C.I.Pigment Blue 15:2, C.I. Pigment Blue 15:3, C.I. Pigment Blue 16 and thelike are included.

As the pigments for green, for example, C.I. Pigment Green 7, C.I.Pigment Green 36 and the like are included.

As the pigments for blue, for example, C.I. Pigment Blue 60, C.I.Pigment Violet 23 and the like are included.

As the pigment for black, for example, C.I. Pigment Black 1, C.I.Pigment Black 6, C.I. Pigment Black 7 and the like are included.

As methods for dispersing the pigments, it is possible to use variousdispersing machines such as a ball mill, sand mill, attritor, roll mill,agitator, Henschel mixer, colloid mill, ultrasonic homogenizer, pearlmill, wet type jet mill and paint shaker. Also it is preferable to use acentrifuging machine and a filter for the purpose of eliminating crudeparticles of a pigment dispersion.

In the ink of the invention, it is one of the characteristics to use apolymeric dispersant for the dispersion of the pigments. The polymericdispersant of the invention is not particularly limited, and awater-soluble resin or a water-insoluble resin is used. As thesepolymeric molecules, it is possible to include polymers made up of asingle monomer or copolymers made up of two or more monomers selectedfrom styrene, styrene derivatives, vinylnaphthalene derivatives, acrylicacid, acrylate derivatives, methacrylic acid, methacrylate derivatives,maleic acid, maleate derivatives, itaconic acid, itaconate derivatives,fumaric acid and fumarate derivatives, and salts thereof. Also, it ispossible to use water-soluble polymeric molecules such as polyvinylalcohol, polyvinyl pyrrolidone, cellulose derivatives, gelatin, andpolyethyleneglycol.

It is preferred that these polymers have both a hydrophilic moiety and ahydrophobic moiety. The hydrophilic moiety has a function to stabilizethe dispersion in water which is a major component of the ink, whereasthe hydrophobic moiety has a function to enhance adhesion onto pigmentsurfaces. Among others, acryl type polymeric dispersants are preferablyused in terms of the characteristics such as easiness of molecularstructure design and easiness to obtain a performance as the dispersant.The acryl type polymeric dispersant is referred to the polymericdispersant containing an acryl type monomer at least at 30 mol % ormore.

As such an acryl type polumeric dispersant, polymers made up of thehydrophobic monomer and hydrophilic monomer shown below, or copolymersmade up of two or more of the monomers, and salts thereof arepreferable. The hydrophobic monomers include but are not limited to, forexample, styrene, α-methylstyrene, methyl methacrylate (MMA), ethylmethacrylate (EMA), propyl methacrylate, n-butyl methacrylate (BMA orNBMA), hexyl methacrylate, 2-ethylhexyl methacrylate (EHMA), octylmethacrylate, lauryl methacrylate (LMA), stearyl methacrylate, phenylmethacrylate, hydroxyethyl methacrylate (HEMA), hydroxypropylmethacrylate, 2-ethoxyethyl methacrylate, methacrylonitrile,2-trimethylsiloxyethyl methacrylate, glycidyl methacrylate (GMA),p-tolyl methacrylate, sorbyl methacrylate, methyl acrylate, ethylacrylate, propyl acrylate, butyl acrylate, hexyl acrylate, 2-ethylhexylacrylate, octyl acrylate, lauryl acrylate, stearyl acrylate, phenylacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, acrylonitrile,2-trimethylsiloxyethyl acrylate, glycidyl acrylate, p-tolyl acrylate,sorbyl acrylate, benzyl acrylate, benzyl methacrylate, 2-phenylethylmethacrylate and the like.

As the hydrophobic monomer, styrene, methyl methacrylate, butylmethacrylate, 2-ethylhexyl methacrylate, benzyl methacrylate,2-phenylethyl methacrylate, or benzyl acrylate is particularlypreferable.

The hydrophilic monomers include, but are not limited to, for example,methacrylic acid (MAA), acrylic acid, maleic acid, dimethylaminoethylmethacrylate (DMAEMA), diethylaminoethyl methacrylate,tert-butylaminoethyl methacrylate, dimethylaminoethyl acrylate,diethylaminoethyl acrylate, dimethylaminopropyl methacrylamide,methacrylamide, acrylamide, dimethyl acrylamide and the like.

As the hydrophilic monomer, methacrylic acid, acrylic acid ordimethylaminoethyl methacrylate is preferable.

A polymeric molecule containing an acid is manufactured directly from anunsaturated acid or manufactured from a blocked monomer having ablocking group which can be eliminated after polymerization. As examplesof the blocked monomer which produces acrylic acid or methacrylic acidafter eliminating the blocking group, trimethylsilyl methacrylate(TMS-MAA), trimethylsilyl acrylate, 1-butoxyethyl methacrylate,1-ethoxyethyl methacrylate, 1-butoxyethyl acrylate, 1-ethoxyethylacrylate, 2-tetrahydropyranyl acrylate, 2-tetrahydropyranyl methacrylateand the like are included.

Structures of these polymers include random polymer or random copolymer,block copolymer, branched polymer or copolymer, graft polymer orcopolymer. Among others, the block copolymer and the branched copolymerare preferable for the object of the invention because the design andcontrol of the hydrophilic and hydrophobic moieties are easy.

The block polymers include structures such as AB, BAB and ABC types(here, A, B and C schematically represent high molecular blocksdifferent in structure one another), but there is no restriction of thestructure so long as the block moiety is present. Particularly, theblock polymer having a hydrophobic block and a hydrophilic block orhaving a balanced block size which contributes to dispersion stabilityis preferable. A functional group can be incorporated in the hydrophobicblock (block to which a coloring agent is bound) thereby improving thedispersion stability, and thus a specific interaction between thedispersant and the coloring agent is further enforced.

These polymers can be synthesized by conventionally known in the art,and can be synthesized particularly by the methods disclosed in thespecification of U.S. Pat. Nos. 5,085,698, 5,221,334, 5,272,201,5,519,085 and 6,117,921, and the examples in JP-Tokukaihei-10-279873A,11-269418A, JP-Tokukai-2001-115065A, 2001-139849A, 2001-247796A and2003-260348A.

As the hydrophobic monomers which can be used for the block copolymer,for example, it is possible to include the same monomers as thehydrophobic monomers which can be used for the acryl type polymericdispersant.

As the hydrophobic monomers, methyl methacrylate, butyl methacrylate,2-ethylhexyl methacrylate, benzyl methacrylate, 2-phenylethylmethacrylate, or benzyl acrylate is particularly preferable. As thehydrophobic high molecular block, the polymer made up of the abovesingle monomer or the copolymer block made up of two or more monomers ispreferable.

As the hydrophilic monomers which can be used for the block copolymer,for example, it is possible to include the same monomers as thehydrophilic monomers which can be used for the acryl type polymericdispersant.

The hydrophilic monomer is preferably methacrylic acid, acrylic acid ordimethylaminoethyl methacrylate, and as the hydrophilic polymer highmolecular block, the polymer made up of the above single monomer orhomopolymer and copolymer made up of two or more of the monomers arepreferable.

As the monomers which can be used for the branched polymer or copolymerand the graft polymer or copolymer, it is possible to use those includedas the monomers which can be used for the above block copolymer. Thebranched polymer or copolymer and the graft polymer or copolymer can beeasily synthesized by using a macromer having a polymerizable functionalgroup at one end, for example, silicone macromer, styrene type macromer,polyester type macromer, polyurethane type macromer or polyalkylethermacromer. As examples of the above macromer, styrene macromers AS-6 andAN-6 supplied from Toagosei Co., Ltd., silicone macromers FM-0711 andFM-0721 supplied from Chisso Corporation, polyethyleneglycol andpolyethyleneglycol methacrylate and the like are included.

A weight average molecular weight of these polymeric molecules ispreferably in the range of 1,000 to 30,000, and more preferably in therange of 1,500 to 15,000. An acid value is preferably in the range of 10to 500, and more preferably in the range of 50 to 250.

In the ink of the invention, a pigment dispersant known in the art, forexample, surfactants such as higher fatty acid salts, alkyl sulfatesalts, alkyl ester sulfate salts, alkyl sulfonate salts, sulfosuccinatesalts, naphthalene sulfonate salts, alkyl phosphate salts,polyoxyalkylenealkylether phosphate salts, polyoxyalkylenealkylphenylether, polyoxyethylenepolyoxypropyleneglycol, glycerin ester, sorbitanester, polyoxyethylene fatty acid amide and amine oxide may be combinedalong with the above polymeric dispersant.

In the aqueous ink of the invention, a volume average particle size of apigment dispersion is preferably from 20 to 200 nm in terms of obtainingpreferable color tone, high print density or good gloss, and morepreferably from 40 to 140 nm in terms of additionally improving lightresistance.

In the invention, the volume average particle size of the pigmentdispersion can be obtained by a commercially available particle sizemeasuring instrument using a light scattering method, electrophoresis, alaser Doppler method and the like, and as a specific particle sizemeasuring instrument, for example, it is possible to include Zetasizer1000HS supplied from Malvern Instruments.

The water-soluble organic solvents which can be used in the inventionspecifically include alcohols (e.g., methanol, ethanol, propanol,isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol,pentanol, hexanol, cyclohexanol, benzyl alcohol, etc.), polyvalentalcohols (e.g., ethyleneglycol, diethyleneglycol, triethyleneglycol,polyethyleneglycol, propyleneglycol, dipropyleneglycol,polypropyleneglycol, butyleneglycol, hexanediol, pentanediol, glycerin,hexanetriol, thiodiglycol, etc.), polyvalent alcohol ethers (e.g.,ethyleneglycol monomethylether, ethyleneglycol monoethylether,ethyleneglycol monobutylether, ethyleneglycol monophenylether,diethyleneglycol monomethylether, diethyleneglycol monoethylether,diethyleneglycol monobutylether, diethyleneglycol dimethylether,propyleneglycol monomethylether, propyleneglycol monobutylether,ethyleneglycol monomethylether acetate, triethyleneglycolmonomethylether, triethyleneglycol monoethylether, triethyleneglycolmonobutylether, triethyleneglycol dimethylether, dipropyleneglycolmonopropylether, tripropyleneglycol dimethylether, etc.), amines (e.g.,ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine,N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine,diethylenediamine, triethylenetetramine, tetraethylenepentamine,polyethyleneimine, pentamethyldiethylenetriamine,tetramethylpropylenediamine, etc.), amides (e.g., formamide,N-N-dimethylformamide, N,N-dimethylacetamide, etc.), heterocycles (e.g.,2-pyrrolidone, N-methyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone,2-oxazolidone, 3-dimethyl-2-imidazolidinone, etc.), sulfoxides (e.g.,dimethylsulfoxide, etc.), sulfones (e.g., sulforane, etc.), sulfonatesalts (e.g., sodium 1-butylsulfonate salt, etc.), acetonitrile, acetone,and the like.

It is also preferred that the respective colored inks according to theinvention contain urea or an urea derivative. By containing urea or theurea derivative in the respective colored inks according to theinvention, it is preferable because it is possible to inhibitaggregation of the pigment particles in the jetted ink liquid drops onthe recording medium and consequently improve glossiness and texture. Itis preferred that this urea or urea derivative has appropriately stronginteraction for expressing objective effects by the interaction such ashydrogen bonds. As such compounds, urea, thiourea, and urea derivativessubstituted with lower alkyl group (e.g., methylurea, dimethylurea,butylurea, ethyleneurea, phenylurea, etc.) are preferable, andparticularly urea and ethyleneurea are preferable.

In the respective colored inks according to the invention, it ispreferred in the light of being capable of obtaining the images withfavorable output stability and high density having preferable gloss thata content of urea is from 1 to 20% by mass.

In the ink according to the invention, pH is preferably 7.0 or above,and more preferably from 8.0 to 10.0. By making the above pH, the imagewhere injection stability is good and print density is high and having apreferable gloss can be obtained, and thus it is preferable. As a pHadjuster used for the color ink according to the invention, for example,various organic amine such as monoethanolamine, diethanolamine andtriethanolamine, inorganic alkali agents such as hydroxide of alkalimetal such as sodium hydroxide, lithium hydroxide and potassiumhydroxide, organic acids and mineral acids.

It is preferable that a surface tension of the ink according to theinvention is from 30 to 50 mN/m. When the surface tension of the inkbecomes less than 30 mN/m, a absorption speed to the recording mediumbecomes fast and aggregation by pigment particles one another occursresulting in occurrence of bronzing and reduction of gloss andscratch/abrasion resistance. When the surface tension exceeds 50 mN/m,color turbidity due to long retention of jetted ink droplets on themedium occurs, and it becomes impossible to obtain the image at highdefinition.

For the surface tension, it is possible to adjust to the desired surfacetension by appropriately conditioning types and addition amounts usingthe various water-soluble organic solvents described above and varioussurfactants described below.

The method of measuring the surface tension is described in generalreference books of surface chemistry and colloid chemistry, for example,Shin Jikken Kagaku Kouza, Vol. 18 (Surface and Colloid) edited by theChemical Society of Japan and published by Maruzen Co., Ltd.: pages 68to 117 can be referred, and specifically, it can be obtained by a ringmethod (DuNouy method) or a plate method (Wilhelmy method).

As one of ways to accomplish the above surface tension, varioussurfactants can be used. Various surfactants which can be used in theinvention are not particularly limited, and for example, include anionicsurfactants such as dialkyl sulfosuccinate salts, alkylnaphthalenesulfonate salts and fatty acid salts, nonionic surfactants such aspolyoxyethylene alkylethers, polyoxyethylene alkylallylethers,acetyleneglycols, block copolymer of polyoxyethylene andpolyoxypropylene, and cationic surfactants such as alkylamine salts, andquaternary ammonium salts. Particularly, the anionic surfactants and thenonionic surfactants can be preferably used.

In the invention, it is preferred that acetylene type surfactant is usedas the surfactant in terms of being capable of obtaining the image wherethe injection stability is good with high print density, havingpreferable gloss and which is excellent in uniformity.

The acetylene type surfactant is not particularly limited, for example,includes acetylene glycols and acetylene alcohols, is more preferablythe surfactant having acetylene group and alkylene oxide chain, and forexample, can include Surfynol 465 (supplied from Nisshin ChemicalIndustry Co., Ltd.).

In the ink of the invention, in addition to the above illustration, ifnecessary, various additives known in the art, for example, a viscosityadjuster, specific resistance adjuster, film forming agent, ultravioletray absorbent, anti-oxidant, anti-color fading agent, antimicrobials andfungicides, anti-rusting agent and the like can be used for the purposeof the injection stability, compatibility of the recording head 22 andink cartridge, storage stability, image permanence, and the otherperformance improvement. For example, as these additives it is possibleto include oil droplet fine particles such as liquid paraffin, dioctylphthalate, tricresyl phosphate and silicon oil, the ultraviolet rayabsorbents described in JP-Tokukaisho-57-74193A, JP-Tokukaisho-57-87988Aand JP-Tokukaisho-62-261476A, the anti-color fading agents described inJP-Tokukaisho-57-74192A, 57-87989A, 60-72785A, 61-146591A,JP-Tokukaihei-1-95091A and 3-13376A, the fluorescent brightening agentsdescribed in JP-Tokukaisho-59-42993A, 59-52689A, 62-280069A, 61-242871Aand JP-Tokukaihei-4-219266A, and the like.

Then, the recording medium of the invention is illustrated.

Generally, as an ink absorbing layer, there are a swelling type and amicro-porous type by broadly dividing. As the swelling type, awater-soluble binder, for example, gelatin, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene oxide and the like is applied alone or incombination, and this is made the ink absorbing layer. However, in theinvention, in order to adapt to continuous high speed print, therecording medium where an ink absorption speed is high is more suitable,and thus from this point, the inkjet recording medium having the inkabsorbing layer of the micro-porous type is used.

In the recording medium having the ink absorbing layer of themicro-porous type (also referred to as a micro-porous layer) of theinvention, it is one of the characteristics that a transferred amount at0.04 seconds of absorption time by Bristow method is 10 ml/m² or more,and it is preferably 10 ml/m² or more and 30 ml/m² or less. When thetransferred amount is less than 10 ml/m², the ink absorption speed onthe recording medium is reduced, color turbidity occurs when the jettedink droplets are printed side by side, and it becomes impossible toobtain the image at high definition.

In the recording medium of the invention, the method to accomplish thetransferred amount defined above is not particularly limited, and thetransferred amount can be used by appropriately conditioning a thicknessof the micro-porous layer, a mean particle size of inorganic fineparticles (F) which configure the micro-porous layer, a type of ahydrophilic binder (B), a ratio (F/B) of the inorganic fine particles tothe hydrophilic binder (B), a type of a support used and the like.

Bristow method referred to in the invention is the method of measuringliquid absorption behavior of paper and plate paper in a short time.Particularly, according to J. TAPPI paper pulp test method No. 51-87, amethod of testing absorbability of the paper or plate paper (Bristowmethod), the measurement is performed, and the absorption is representedby the transferred amount (ml/m²) at 0.04 sec of the absorption time. Inthe above method, purified water (ion-exchange water) is used for themeasurement. However, in order to make determination of a measurementarea easy, in the invention, the measurement is performed using anaqueous solution of 2% C.I. Acid Red 52.

One example of specific measurement method is illustrated below.

As the method of measuring the transferred amount, after leaving therecording medium under an atmosphere of 25° C. and 50% RH for 12 hoursor more, the measurement is performed using a Bristow testing machine IItype (press mode) which is a liquid dynamic absorbability testingmachine supplied from Kumagai Rikikogyo Co., Ltd. The aqueous solutionof 2% C.I. Acid Red 52 is used for the measurement as mentioned above toenhance measurement accuracy, and the transferred amount can be obtainedby measuring an area stained on the recording medium after a definedcontact time.

As for a recording medium according to the present invention, it is acharacteristic that the 20-degree specular gloss according to JIS-Z-8741is 20 to 45%.

The 20-degree specular gloss is a 20-degree specular gloss value (%)measured according to the method provided in JIS-Z-8741. A speculargloss correlates with the smoothness of a surface of recording media. Asmoother surface has a higher specular gloss value. Therefore in case ofa 20-degree specular gloss less than 20%, the smoothness of the surfaceof recording media is inadequate and forming a pigment image thereonleads to decreasing gloss of the image as a whole. Increase of theamount of adhered pigment cause increase of the specular gloss. In thiscase, if a white background part (surface of recording media) with nopigment adhered has a specular gloss less than 20%, gloss differencebetween the image part and the no-image part becomes larger and only theimage part stands out in bold relief.

Meanwhile, when trying to manufacture the recording medium where the20-degree specular gloss exceeds-45%, numerous energy is required tomake the surface smooth, and it becomes unrealistic. Furthermore, whenthe surface is made smooth such that the 20-degree specular glossexceeds 45%, the micro-porous layer of the recording medium is crushed,the absorption speed and the absorption capacity are reducedconsequently leading to color turbidity at the image formation, and itbecomes impossible to obtain the image with high definition. Thus, bymaking the 20-degree specular gloss between 20% and 45%, it is possibleto inhibit a phenomenon where only the image section stands out in boldrelief, which is unique for the image formed by the pigment inks, andimprove depth feel of the whole image. Also, it is possible to form theimage with high definition without causing the color turbidity. As aresult, it becomes possible to obtain the images which come near thesilver salt photographs.

The 20-degree specular gloss according to the invention can be measuredusing, for example, precision glossmeters GM-26D, True Gloss GM-26DPROand a variable angle glossmeter GM-3D (supplied from Murakami ColorResearch Laboratory), variable angle glossmeters VGS-10001DP, VG-2000(supplied from Nippon Denshoku Industries Co., Ltd.), a digital variableangle glossmeter (supplied from Suga Test Instruments Co., Ltd.) and thelike.

In the recording medium according to the invention, a way for realizingthe 20 degree specular gloss value (%) within the scope defined in theinvention is not particularly limited, but, for example, the desired 20degree specular gloss value (%) can be obtained by the method ofpreviously giving a smoothing treatment to a support surface and formingan ink absorption layer thereon, the method of installing the inkabsorption layer on the smooth support where boric acid has beenpreviously impregnated, the method of installing a polymer fine particlelayer on an ink absorption layer surface and smoothing by treatment withheat and pressure, the method of installing a gloss layer made up ofinorganic fine particles and a binder on the ink absorption layersurface, the method of applying the ink absorption layer andsubsequently performing the smoothing treatment such as a calendartreatment, and the like. For example, in the case of surface smoothingby a specular roll, it is preferable to perform typically at about 20 to100° C. with a line pressure of 0.5 to 4 kN/cm, at a feeding velocity of10 to 500 m/min as a calendar condition and dry at about 20 to 100° C.for about 0.1 to 10 min.

Hereinafter, respective constituent factors of the inkjet recordingmedium of the invention are illustrated.

Conventionally, various methods of forming micro-pores in a membranehave been known, for example, the method of forming micro-pores byapplying a uniform coating solution containing two or more polymericmolecules onto a support and causing phase separation of these polymericmolecules in a drying process, the method of making micro-pores byapplying a coating solution containing solid fine particles and ahydrophilic or hydrophobic resin onto a support, after drying, immersingan inkjet recording medium in water or a liquid containing anappropriate organic solvent, and dissolving the solid fine particles,the method of forming micro-pores in a membrane by applying a coatingsolution containing a compound having a nature which foams at themembrane formation, and subsequently foaming this compound in a dryingprocess, the method of forming micro-pores in porous fine particles andbetween fine particles by applying a coating solution containing poroussolid fine particles and a hydrophilic binder on a support, the methodof forming micro-pores between solid fine particles by applying acoating solution containing solid fine particles or fine particle oildroplets having a volume nearly equal to or more than that of ahydrophilic binder and the hydrophilic binder on a support, and the likehave been known.

The micro-porous layer of the invention indicates an ink receiving layerwith a void rate of 25 to 75%, and preferably the void rate of 30 to70%, mainly formed from the inorganic fine particles and a small amountof the hydrophilic binder.

In the invention, it is the characteristics that the micro-porous layeris formed by containing the inorganic fine particles with a meanparticle size of 15 to 100 nm, and preferably the mean particle size isfrom 20 to 80 nm. When the mean particle size exceeds 100 nm,deterioration of surface gloss of a coating occurs.

As the inorganic fine particles used for the above purpose, it ispossible to include white inorganic pigments such as calcium carbonatelight, calcium carbonate heavy, magnesium carbonate, kaolin, clay, talc,calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinchydroxide, zinc sulfide, zinc carbonate, hydrotalcite, aluminiumsilicate, diatomite, calcium silicate, magnesium silicate, syntheticamorphous silica, colloidal silica, alumina, colloidal alumina,pseudoboehmite, aluminium hydroxide, lithopone and magnesium hydroxide.

The mean particle size of the inorganic fine particles in the inventionis obtained as the simple mean value (number mean) by observing crosssections and surfaces of the micro-porous layer in the recording mediumby an electron microscope and randomly measuring the particle size of1,000 particles. Here, the particle size of individual particle is adiameter when a circle equal to a projection area thereof is supposed.As the inorganic fine particle, it is preferable to use silica oralumina.

As the silica which can be used in the invention, silica synthesized bya usual wet method, colloidal silica or silica synthesized by a vaporphase method or the like is preferably used, and as the silicapreferably used in the invention, colloidal silica or fine particlesilica synthesized by the vapor phase method is preferable. Amongothers, the fine particle silica synthesized by the vapor phase methodhas a characteristics that a so-called soft aggregation structure isformed by coexisting with the hydrophilic binder to give a high voidrate. Further this fine particle silica when it is added to a cationicpolymer molecule used for the purpose of immobilizing colorants, roughand large aggregation is difficult to be formed, and thus it ispreferable.

Alumina or alumina hydrate which can be used in the invention may becrystalline or amorphous, and it is possible to use those with any shapesuch as undefined shaped particles, spherical particles and needleparticles. Among others, the alumina hydrate having a plate shape wherean average aspect ratio is from 1 to 4 is preferable. There are thosehaving a fibrous shape and those having a plate shape in the aluminahydrate. When the fibrous alumina hydrate is used, it is prone toorientate in parallel with a substrate surface at the application, andthus formed micropores become small. On the contrary, in the case of theplate alumina hydrate, tendency to orientate to a certain direction bythe application is small, and a relatively large void rate can beobtained.

As the hydrophilic binder which can be used in the micro-porous layer ofthe invention, for example, polyvinyl alcohol, gelatin, polyethyleneoxide, polyvinyl pyrrolidone, polyacrylic acid, polyacrylamide,polyurethane, dextran, dextrin, carrageenan (κ, ι, λ, etc.) agar,pullulan, water-soluble polyvinyl butyral, hydroxyethylcellulose,carboxymethylcellulose, and the like are included. It is possible tocombine two or more of these water-soluble binders, butpolyvinyl-alcohol or derivatives thereof are particularly preferable interms of relatively small moisture absorption property of the binder,smaller curl of the medium and being high binder performance by the useof a small amount with excellent crack and velation.

As polyvinyl alcohol preferably used in the invention, modifiedpolyvinyl alcohol such as polyvinyl alcohol where the end is modifiedwith cation, and anion modified polyvinyl alcohol having anionic groupare included in addition to common polyvinyl alcohol obtained byhydrolyzing polyvinyl acetate.

As polyvinyl alcohol obtained by hydrolyzing polyvinyl acetate, thosewith an average polymerization degree of 300 or more are preferablyused, and particularly those with an average polymerization degree of1,000 to 5,000 are preferably used. A saponification degree ispreferably from 70 to 100%, and particularly preferably 80 to 99.8%.

The cation modified polyvinyl alcohol is, for example, the polyvinylalcohol having primary to tertiary amino groups and quaternary aminogroups in a backbone or side chains as described inJP-Tokukaisho-61-10483A, and this is obtained by saponifying a copolymerof an ethylenic unsaturated monomer having cationic group and vinylacetate.

As the ethylenic unsaturated monomer having cationic group, for example,trimethyl-(2-acrylamide-2,2-dimethylethyl)ammonium chloride,trimethyl-(3-acrylamide-3,3-dimethylpropyl)ammonium chloride,N-vinylimidazole, N-methylvinylimidazole,N-(3-dimethylaminopropyl)methacrylamide, hydroxyethyltrimethylammoniumchloride, trimethyl-(3-methacrylamidepropyl)ammonium chloride and thelike are included.

A percentage of cation modified group-containing monomer of the cationmodified polyvinyl alcohol is from 0.1 to 10 mol %, and preferably from0.2 to 5 mol % based on vinyl acetate.

As anion modified polyvinyl alcohol, for example, polyvinyl alcoholhaving anionic group described in JP-Tokukaihei-1-206088A, copolymers ofvinyl alcohol and a vinyl compound having water-soluble group describedin JP-Tokukaisho-61-237681A and 63-307979, and modified polyvinylalcohol having water-soluble group described in JP-Tokukaihei-7-285265Aare included.

As nonionic modified polyvinyl alcohol, for example, polyvinyl alcoholderivatives where polyalkyleneoxide group is added to a part of vinylalcohol described in JP-Tokukaihei-7-9758A, block copolymer of a vinylcompound having hydrophobic group and vinyl alcohol described inJP-Tokukaihei-8-25795A, and the like are included.

Polyvinyl alcohol can be also used in combination with two or moredepending on difference in polymerization degree and modification type.Particularly when polyvinyl alcohol with a polymerization degree of2,000 or more, is used, if it is precedently added at 0.05 to 10% bymass, preferably from 0.1 to 5% by mass based on the inorganic fineparticles and then polyvinyl alcohol with a polymerization degree of2,000 or more is added, there is no remarkable thickening and it ispreferable.

A ratio of the inorganic fine particles to the hydrophilic binder in themicro-porous layer is preferably from 2 to 20 at a mass ratio. When themass ratio is 2 times or more, a porous membrane with sufficient voidrate is obtained, a sufficient void capacity is easily obtained,micro-pores are not occupied by swelling of retainable hydrophilicbinder at the inkjet recording, and thus it becomes a factor capable ofretaining a high ink absorption speed. On the other hand, if this ratiois 20 times or less, when the micro-porous layer is formed by applying athick membrane, it becomes difficult to cause cracks. The particularlypreferable ratio of the inorganic fine particles to the hydrophilicbinder is from 2.5 to 12 times, and most preferably it is from 3 to 10times.

It is preferred that a total amount of the micro-pores (void capacity)in the micro-porous layer is 16 ml or more per m² of the recordingmedium. By making the void capacity 16 ml/m² or more, even when an inkamount becomes large, it is possible to make an ink absorbability good,and thus it is possible to improve the image quality and suppressreduction of drying.

The upper limit of the void capacity is preferably not more than 25ml/m². Though the more micro-pores lead to increase of the absorptionspeed and absorption capacity, on the contrary, at the same time, itbecomes more delicate to an external force. Trying to the increasethickness for this has a problem that a crack is easily generated inproduction. Though it is possible to increase the absorption speed andabsorption capacity by increasing the void rate without changing thethickness, it becomes also delicate to generation of crack. Whereasthere are various studies to overcome the problem, in the presentcircumstance, a thickness or a void rate with the absorption speed perunit area more than 25 ml/m² causes much generation of minute crack. Asa result, it becomes impossible to form a high-quality image. Thereforeit is preferable that a recording medium having a micro-porous layer isdesigned and produced in such a way that the recording medium has athickness or a void rate with an absorption capacity per unit area notmore than 25 ml/m².

The void capacity in the invention indicates a saturated waterabsorption amount obtained by Bristow method. When the transferredamount obtained by Bristow method is plotted versus a square root of theabsorption time, a line with a certain slope is obtained. Thisrepresents changes of absorption amounts of the recording medium versusthe absorption time. When the ink (here, referred to the aqueoussolution of 2% C.I. acid red 52) is absorbed to fill up the voidcapacity, there becomes no room, and thus the slope is 0. The waterabsorption amount at that time is the saturated water absorption amount,and is considered as a value which represents the void capacity. In thecase of the recording medium having an absorbable support preferablyused in the invention, it sometimes represents the absorption of thesupport in addition to the ink absorption by the ink absorbing layer. Inthe recording medium used in the invention, the absorption speed of theink in the ink absorbing layer is overwhelmingly much faster than thatin the support, and thus, even when the absorption by the support ismeasured, a curve has double slopes and discrimination of both is easy.

The void rate referred to in the invention indicates the rate of a totalvolume of the voids in a volume of the micro-porous layer. The voidcapacity obtained by the above Bristow method can be used as it is forthe total volume of the voids. The volume of the micro-porous layer canbe obtained as the volume per m² of the recording medium by measuringthe dried membrane thickness. The aimed void rate can be obtained as aratio of both volumes by calculation. The total volume of the voids canbe easily obtained by the saturated transferred amount and the waterabsorption amount measurement by Bristow method.

For the above micro-porous layer, various additives can be used inaddition to the inorganic fine particles and the binder. Among others, acationic polymeric molecule, hardener, urea or a derivative thereofplays important roles in terms of improving bleeding resistance,bronzing resistance, and scratch/abrasion resistance.

Examples of the cationic polymer molecules include polyethyleneimine,polyallylamine, polyvinylamine, dicyandiamidepolyalkylenepolyaminecondensates, polyalkylenepolyaminedicyandiamide ammonium condensates,dicyandiamideformaline condensates, epichlorohydrin/dialkylamineaddition polymers, diallyldimethylammonium chloride polymers,diallyldimethylammonium chloride/SO₂ copolymers, polyvinylimidazole,vinylpyrrolidone/vinylimidazole copolymers, polyvinylpyridine,polyamidine, chitosan, cationized starch, vinylbenzyltrimethylammoniumchloride polymers, (2-methacroyloxyethyl)trimethylammonium chloridepolymers, dimethylaminoethyl methacrylate polymers, and the like.

Cationic polymeric molecules described in Kagaku Kogyo Jiho (Aug. 15 and25, 1998) and polymeric molecular dye fixing agents described in“Kobunshi Yakuzai Nyumon” published by Sanyo Chemical Industries Ltd.are included as the examples.

In the recording medium according to the invention, it is preferable toadd the hardener of the water-soluble binder which forms themicro-porous layer.

The hardener which can be used for a hard membrane of the water-solublebinder which forms the micro-porous layer in the invention is notparticularly limited so long as it performs a hardening reaction withthe water-soluble binder. Boric acid and salts thereof are preferable,but the other known in the art can be also used. Generally it is thecompound having groups capable of reacting with the water-soluble binderor the compound which facilitates a reaction of different groups oneanother which the water-soluble binder has, and is appropriately useddepending on the type of water-soluble binder. Specific examples of thehardener include epoxy type hardeners (diglycidylethylether,ethyleneglycol diglycidylether, 1,4-butanediol diglycidylether,6-diglycidylcyclohexane, N,N-diglycidyl-4-glycidyloxyaniline, sorbitolpolyglycidylether, etc.), aldehyde type hardeners (formaldehyde,glyoxazol, etc.), active halogen type hardeners(2,4-dichloro-4-hydroxy-1,3,5-s-triadine, etc.), active vinyl typecompounds (1,3,5-trisacryloyl-hexahydro-s-triadine,bisvinylsulfonylmethylether, etc.), aluminium alum, and the like.

Boric acid and salts thereof are referred to oxyacids where boron atomis a central atom and salts thereof, and specifically, ortho-boric acid,diboric acid, metaboric acid, tetraboric acid, pentaboric acid andoctaboric acid and salts thereof are included.

Boric acid having boron atoms and the salts thereof as the hardeners maybe used as an aqueous solution thereof alone or in mixture with two ormore. Particularly preferable is a mixed aqueous solution of boric acidand borax. Aqueous solutions of boric acid and borax are each added onlyby relatively diluted aqueous solutions, but it is possible to make athick aqueous solution by mixing the both, and concentrate the coatingsolution. Besides there is an advantage that pH of the added aqueoussolutions can be controlled relatively freely. A total use amount of theabove hardener is preferably from 1 to 600 mg per g of the abovewater-soluble binder.

It is possible to add polyvalent metal ions to the recording mediumaccording to the invention. The polyvalent metal ion is not particularlylimited so long as it is bivalent or more metal ion, and preferablepolyvalent ions include aluminium ion, zirconium ion, titanium ion andthe like. These polyvalent metal ions can be contained in themicro-porous layer in a water-soluble or water-insoluble salt form.

These polyvalent metal ions may be used alone or in combination withdifferent two or more. The compound comprising the polyvalent metal ionsmay be added to a coating solution which forms the micro-porous layer orsupplied to the micro-porous layer by an over coat method after onceapplying the micro-porous layer, particularly after once applying anddrying the micro-porous layer. As the former, when the compoundcomprising the polyvalent metal ions is added to the coating solutionwhich forms the ink absorbing layer, it is possible to use the method ofadding by uniformly dissolving in water or an organic solvent or a mixsolvent thereof or the method of adding by dispersing into fineparticles by a wet pulverizing method of a sand mill, an emulsifyingdispersion method and the like. When the micro-porous layer is made upof multiple layers, they may be added to the coating solution for onlyone layer or can be added to the coating solutions for two or more layeror all constitutive layers. As the latter, when they are added by theover coat method after once forming the micro-porous layer, it ispreferred that the compound comprising the polyvalent metal ions isuniformly dissolved in the solvent, and subsequently supplied to themicro-porous layer.

These polyvalent metal ions are used in the range of about 0.05 to 20mmol, and preferably from 0.1 to 10 mmol per m² of the recording medium.

To the micro-porous layer according to the invention, various additivesother than the above can be added. For example, it is possible tocontain various additives known in the art such as polystyrene,polyacrylate esters, polymethacrylate esters, polyacrylamides,polyethylene, polypropylene, polyvinyl chloride, polyvinylidenechloride, or copolymers thereof, urea resins, or organic latex fineparticles of melamine resins, various cationic or nonionic surfactants,ultraviolet ray absorbents described in JP-Tokukaisho-57-74193A,57-87988A and 62-261476A, anti-color fading agents described inJP-Tokukaisho-57-74192A, 57-87989A, 60-71785A, 61-146591A,JP-Tokukaihei-1-95091A and 3-13376A, fluorescent brightening agentsdescribed in JP-Tokukaisho-59-42993A, 59-52689A, 62-280069A, 61-242871Aand JP-Tokukaihei-4-219266A, pH adjusters such as sulfuric acid,phosphoric acid, citric acid sodium hydroxide, potassium hydroxide andpotassium carbonate, ant-foaming agent, preservative, thickening agent,anti-electrostatic agent and matting agent.

Both an absorbable support and non-absorbable support can be used as thesupport of the recording medium according to the invention. In terms ofexerting objective effects of the invention with no obstacle, forexample, it is preferable to use the absorbable support which is a papersupport such as plain paper, baryta paper, art paper, coated paper andcast-coated paper.

The absorbable support of the invention can include, for example, sheet,plate and the like having common paper, synthetic paper, fabrics, woodmaterials and the like, and particularly the paper is the mostpreferable because it is excellent in absorbability of the substrateitself and cost. The paper support is illustrated below.

As basic materials of the paper support, it is possible to use thosewhere a major basic material is wood pulps such as chemical pulps suchas LBKP and NBKP, mechanical pulps such as GP, CGP, RMP, TMP, CTMP, CMPand PGW, and used paper pulps such as DIP, and it is preferable to usehardwood pulps. As the hardwood pulps, kraft pulp, sulfate pulp,chemithermomechanical pulp, chemimechanical pulp and the like may beused alone or in combination with several types. If necessary, papermaking is performed by using synthetic pulp such as polypropylene orsynthetic fibers such as nylon and polyester in addition to the woodpulps.

In terms of improving whiteness degree, it is preferred that a bleachingtreatment by peroxide and the like is given to the pulp which is a basicmaterial. It is preferred that the bleaching treatment is given afterdigesting the pulp, subsequent chlorine treatment, alkali treatment orextraction, hypochlorite bleaching, chlorine dioxide bleaching, andmultistage bleaching by combination thereof, further if necessaryreduction bleaching by hydrosulfite and sodium borohydride. Morepreferably, peroxide bleaching treatment in alkali could be given as thefinal pulp bleaching treatment after the pulp bleaching treatments knownin the art after digesting the pulp, but the alkali treatment orextraction or purification may be further given.

Various additives conventionally known in the art such as a sizingagent, pigments, paper power enhancer, fixing agents, fluorescentbrightening agent, wet paper power agent and cationizing agent can beadded to the paper support if necessary. As the sizing agent, the sizingagents such as a higher fatty acid, alkylketene dimer, rosin, paraffinwax, alkenylsuccinic acid and petroleum resin emulsion can be added ifnecessary. The pigments include calcium carbonate, talc, titanium oxide,urea resin fine particles and the like, the paper power enhancersinclude starch, polyacrylamide, polyvinyl alcohol and the like, and thefixing agents include sulfate band and cationic polymeric moleculeelectrolytes, but they are not limited thereto.

The paper support can be manufactured by mixing the above fibersubstances such as wood pulps and various additives and using variouspaper making machines such as a fourdrinier machine, cylinder machineand twin wire paper making machine. If necessary, it is also possible togive a size press treatment by starch, polyvinyl alcohol and the like,various coating treatments and calendar treatment in the paper makingstage or after the paper making.

A paper density is generally from 0.7 to 1.2 g/cm³ (JIS-P-8118). A basepaper stiffness is preferably from 20 to 200 g under the conditiondefined in JIS-P-8143.

A paper pH is preferably from 5 to 9 when measured a hot waterextraction method defined in JIS-P-8113.

In the invention, for the purpose of increasing an adhesion strength ofthe support and the ink receiving layer, it is possible to give coronadischarge treatment, undercoating treatment and application of anintermediate layer prior to the application of the ink receiving layer.

Next, the method of manufacturing the inkjet recording medium of theinvention is illustrated.

As the method of manufacturing the inkjet recording medium of theinvention, it is possible to manufacture by appropriately selecting anapplication mode from the application modes known in the art andapplying and drying respective constituent layers comprising the inkabsorbing layer onto the support separately or simultaneously. As theapplication mode, for example, a roll coating method, rod bar coatingmethod, air knife coating method, spray coating method, curtainapplication method, or a slide bead application method using a hopperdescribed in U.S. Pat. Nos. 2,761,419 and 2,761,791, an extrusion coatmethod and the like are preferably used.

As a viscosity when a simultaneous overlaying application is performed,in the case of using the slide bead application mode, it is preferablyin the range of 5 to 100 mPa·s, and more preferably from 10 to 70 mPa·s.In the case of using the curtain application mode, it is preferably inthe range of 5 to 1200 mPa·s, and more preferably from 25 to 500 mPa·s.

The viscosity of the coating solution at 15° C. is preferably 100 mPa·sor more, more preferably from 100 to 30,000 mPa·s, still preferably from3,000 to 30,000 mPa·s, and most preferably from 10,000 to 30,000 mPa·s.

As the applying and drying methods, it is preferred that the coatingsolution is heated to 30° C. or above, the simultaneous overlayingapplication is performed, subsequently a temperature of a formed coatingfilm is once cooled to 1 to 15° C., and the drying is performed at 10°C. or above. More preferably, a drying condition is that the drying isperformed at the condition in the range of a wet bulb temperature of 5to 50° C. and a membrane surface temperature of 10 to 50° C. Coolingimmediately after the application is preferably performed by ahorizontal set mode in terms of formed coating film uniformity.

EXAMPLES

Hereinafter, the present invention is specifically illustrated byreferring to Examples, but the invention is not limited thereto.

<<Manufacture of Recording Medium™>>

[Manufacture of Recording Medium 1]

[Manufacture of Support]

Base paper was made by preparing a slurry solution containing 1 part ofpolyacrylamide, 4 parts of ash (talc), 2 parts of cationized starch, 0.5parts of polyamide epichlorohydrin resin and various addition amounts ofalkylketene dimer (sizing agent) for 100 parts of wood pulp(LBKP/NBSP=50/50) and using a fourdrinier machine such that a weighingis 170 g/m². A support which was an absorbable support having a smoothsurface was made by giving a super calendar treatment to this basepaper. Additionally an aqueous solution of 3% boric acid was applied anddried by a roll coater and a support 1 impregnated with 0.1 g/m² ofboric acid was manufactured.

After giving corona discharge to this support 1, a hardener-containinggelatin undercoating layer was applied at 0.04 g/m² in terms of a solidcontent, and on a back face, a styrene/acryl type emulsion containingsilica fine particles (matting agent) having a mean particle size of 1μm and a small amount of a cationic polymeric molecule (conductingagent) was applied such that a dried film thickness is about 0.5 μm.

[Preparation of Coating Solution for Ink Absorbing Layer]

A coating solution for an ink absorbing layer (micro-porous layer) wasprepared according to the following procedure.

[Preparation of Titanium Oxide Dispersion]

Titanium oxide (20 kg) (W-10 supplied from Ishihara Sangyo Co., Ltd.)having a mean particle size of 0.25 μm was added to 90 L of an aqueoussolution at pH 7.5 containing 150 g of sodium tripolyphosphate, 500 g ofpolyvinyl alcohol (PVA235 supplied from Kuraray Co., Ltd.), 150 g ofcationic polymeric molecule P-1 (refer to the following Chemicalformula) and 10 g of anti-foaming agent SN 381 supplied from San nobukoKK, dispersed by a high pressure homogenizer (Sanwa Industries Co.,Ltd.), and subsequently a total amount was filled up to 100 L to yield auniform titanium oxide dispersion.

(PREPARATION OF SILICA DISPERSION 1) Water 71 L Boric acid 0.27 kg Borax0.24 kg Ethanol 2.2 L Aqueous solution of 25% cationic polymericmolecule P-1 17 L Aqueous solution of 10% anti-color fading agent (AF1*1) 8.5 L Aqueous solution of fluorescent brightening agent (*2) 0.1 L

A total amount was filled up to 100 L with purified water.

As inorganic fine particles, 50 kg of silica fine particles (meanprimary particle size: about 35 nm) were prepared, the above additiveswere added thereto, and subsequently the dispersion was performed by adispersion method described in Example 5 of JP-Tokukai-2002-47454A toyield a silica dispersion 1.

-   -   1: Anti-color fading agent (AF-1) HO—N(C₂H₄SO₃Na)₂    -   2: UVITEX NFW LIQUID supplied from Ciba Specialty Chemicals Inc.        (Preparation of Silica Dispersion 2)

A silica dispersion 2 was prepared as is the case with the preparationof the above silica dispersion 1, except that the cationic polymericmolecule P-1 was changed to a cationic polymeric molecule P-2 (refer tothe following Chemical formula).

(Preparation of Coating Solution)

Respective coating solutions of the first, second, third and fourthlayers were prepared by the following procedures.

<Coating Solution for First Layer>

The following additives were sequentially added to 610 ml of the silicadispersion 1 at 40° C. with stirring. Aqueous solution of 5% polyvinylalcohol (PVA235 220 ml supplied from Kuraray Co., Ltd.) Aqueous solutionof 5% polyvinyl alcohol (PVA245 80 ml supplied from Kuraray Co., Ltd.)Titanium oxide dispersion 30 ml Polybutadiene dispersion (mean particlesize: about 15 ml 0.5 μm, solid concentration: 40%) Aqueous solution of5% surfactant (SF1) 1.5 ml

A total amount was filled up to 1000 ml with purified water.

<Coating Solution for Second Layer>

The following additives were sequentially added to 630 ml of the silicadispersion 1 at 40° C. with stirring. Aqueous solution of 5% polyvinylalcohol (PVA235 180 ml supplied from Kuraray Co., Ltd.) Aqueous solutionof 5% polyvinyl alcohol (PVA245 80 ml supplied from Kuraray Co., Ltd.)Polybutadiene dispersion (mean particle size: about 15 ml 0.5 μm, solidconcentration: 40%)

A total amount was filled up to 1000 ml with purified water.

<Coating Solution for Third Layer>

The following additives were sequentially added to 650 ml of the silicadispersion 2 at 40° C. with stirring. Aqueous solution of 5% polyvinylalcohol (PVA235 180 ml supplied from Kuraray Co., Ltd.) Aqueous solutionof 5% polyvinyl alcohol (PVA245 80 ml supplied from Kuraray Co., Ltd.)

A total amount was filled up to 1000 ml with purified water.

<Coating Solution for Fourth Layer>

The following additives were sequentially added to 650 ml of the silicadispersion 2 at 40° C. with stirring. Aqueous solution of 5% polyvinylalcohol (PVA235 180 ml supplied from Kuraray Co., Ltd.) Aqueous solutionof 5% polyvinyl alcohol (PVA245 80 ml supplied from Kuraray Co., Ltd.)Aqueous solution of 50% saponin 4 ml Aqueous solution of 5% surfactant(SF1) (refer to the 6 ml following Chemical formula)

A total amount was filled up to 1000 ml with purified water.

The two step filtration of the respective coating solutions prepared asabove was performed with a 20 μm filter capable of collecting.

All of the above coating solution exhibited viscosity property of 30 to80 mPa·s at 40° C. and 30,000 to 100,000 mPa·s at 15° C.

(Application)

The respective coating solutions obtained in this way weresimultaneously applied on an upper side of the above support made aboveto arrange in order of the first layer (35 μm), the second layer (45μm), the third layer (45 μm) and the fourth layer (40 μm). A number in aparenthesis indicates a wet film thickness. The application wassimultaneously performed at an application width of about 1.5 m at anapplication speed of 100 m/min using each coating solution at 40° C. andusing a 4-layer type curtain coater, and then was calendered by aspecular roll.

Immediately after the application, cooling was performed in a coolingzone retained at 8° C. for 20 sec, and subsequently drying was performedby blowing respective drying winds at 20 to 30° C. and a relativehumidity of 20% or less for 30 sec, at 60° C. and a relative humidity of20% or less for 120 sec, and at 55° C. and a relative humidity of 20% orless for 60 sec. Then the surface was calendered, and additionally, arecording medium 1 was obtained by performing air conditioning in an airconditioning zone at 23° C. and relative humidity of 40 to 60%, androlling up in a roll shape. The obtained recording medium 1 was thenstored in a roll shape at 40° C. for 5 days with being humidified, andsubsequently cut into a given size. As a result of measuring by themethod described below, the void rate of the recording medium was 55%.Also as a result of measuring by the method described below, thetransferred amount at 0.04 seconds of absorption time by Bristow methodwas 16 ml/m². According to JIS-Z-8741, the 20-degree specular gloss onthe side of an ink absorbing layer provided surface was measured by adigital variable angle glossmeter (supplied from Suga Test InstrumentsCo., Ltd.), and consequently it was 24%.

[Manufacture of Recording Medium 2]

A recording medium 2 where the transferred amount at 0.04 seconds ofabsorption time by Bristow method was 8 ml/m² was made by changing thesupport 1 to the following support 2 and appropriately changing aconstituent ratio (F/B) of silica fine particles (F) to polyvinylalcohol (B) in the respective ink absorbing layers in the manufacture ofthe above recording medium 1.

(Manufacture of Support 2)

Base paper was made by preparing a slurry solution containing 1 part ofpolyacrylamide, 4 parts of ash (talc), 2 parts of cationized starch, 0.5parts of polyamide epichlorohydrin resin and various addition amount ofalkylketene dimer (sizing agent) for 100 parts of wood pulp(LBKP/NBSP=50/50) and using a fourdrinier machine such that a weighingis 170 g/m². After giving a calendar treatment to this base paper, a lowdensity polyethylene resin with a density of 0.92 containing 7% anatasetype titanium oxide and a small amount of a color tone adjuster wascoated on a single side of the base paper by a melting extrusion coatingmethod such that a thickness is 28 μm at 320° C. Immediately after themelting extrusion application, various fine particle typing treatmentswas given to the surface of polyethylene by pressing/cooling a coolingroll having various regular concavoconvex height. Difference of thetyping was made by conditioning the density and the concavoconvexheight.

Then, a support 2 which was non-absorbable support was made by coating amelted matter where high density polyethylene with a density of 0.96 andlow density polyethylene with a density of 0.92 were mixed at 70/30 onan opposite side face similarly by the melting extrusion coating methodsuch that a thickness was 32 μm.

After giving corona discharge to a face side of the layer containingtitanium oxide of this support 2, a hardener-containing gelatinundercoating layer was applied at 0.04 g/m² in terms of a solid content,and on a back face, a styrene/acryl type emulsion containing silica fineparticles (matting agent) having a mean particle size of 1 μm and asmall amount of a cationic polymeric molecule (conducting agent) wasapplied such that a dried film thickness was about 0.5 μm.

[Manufacture of Recording Medium 3]

A recording medium 3 where the transferred amount at 0.04 seconds ofabsorption time by Bristow method was 20 ml/m² was made by appropriatelychanging a constituent ratio (F/B) of silica fine particles to polyvinylalcohol in the respective ink absorbing layers in the manufacture of theabove recording medium 2.

[Manufacture of Recording Medium 4]

A recording medium 4 where the transferred amount at 0.04 seconds ofabsorption time by Bristow method was 11 ml/m² was made by appropriatelychanging a constituent ratio (F/B) of silica fine particles to polyvinylalcohol in the respective ink absorbing layers in the manufacture of theabove recording medium 1. The void rate was measured by the methoddescribed below, and it was 35%

[Manufacture of Recording Medium 5] Alumina hydrate (Disperal HP18supplied from Sasol 0.50 kg Ltd.) Purified water 10 L

Hydrochloric acid at 1 mol/L was added to the above dispersion to adjustpH to 4, and this was stirred at 95° C. for 2 hours. Then, an aqueoussolution of sodium hydroxide at 1 mol/L was added to adjust pH to 10,and further stirred for 8 hours. After stirring, the solution was cooledto room temperature, pH was adjusted to 7 to 8, desalting treatment wasgiven, and further acetic acid was added to deflocculate. Afterconcentrating until a solid content became 17%, an aqueous solution of9% polyvinyl alcohol (PVA117 supplied from Kuraray Co., Ltd.) was mixedsuch that a solid content ratio of alumina to polyvinyl alcohol was 10:1at a weight ratio, and stirred to yield a coating solution.

The coating solution prepared as the above was filtrated with a 20 μlfilter capable of collecting. This coating solution was applied onto asupercalendered baryta layer of a substrate (whiteness degree: 89%) by adie coater such that a dried film thickness was 30 g/m². Note that thesubstrate was coated with an aqueous boric acid solution and dried inadvance in such a way that the boric acid content is 0.5 g/m². Anapplying speed at that time was 50 m/min and the drying was performed ata temperature of 150° C. to make a recording medium 5.

The mean particle size of the alumina particles in the recording medium5 was 30 nm. The transferred amount at 0.04 seconds of absorption timeby Bristow method was 22 ml/m², and the void rate was 55%

[Manufacture of Recording Media 6 to 8]

Recording media 6 to 8 were made as was the case with the manufacture ofthe recording medium 1, except that the silica particles (mean particlesize: about 35 nm) used for the preparation of the respective inkabsorbing layer coating solutions were changed to silica particles withmean particle size described in Table 1. The transferred amounts and thevoid rates of these recording media were as was shown in Table 1.

[Manufacture of Recording Medium 9]

A recording medium 9 was made as was the case with the manufacture ofthe recording medium 1, except that boric acid and borax used for thepreparation of the respective ink absorbing layer coating solutions wereremoved.

[Manufacture of Recording Media 10 and 11]

Recording media 10 and 11 were made as was the case with the manufactureof the recording medium 1, except that the void rates of the inkabsorbing layer were 25% and 75%, respectively by appropriately changingthe constituent ratio (F/B) of the silica fine particles to polyvinylalcohol in the respective ink absorbing layers. The void rates in theserecording media were as was shown in Tables 1 and 2.

[Manufacture of Recording Media 12 to 15]

Recording media 12 to 15 were made as was the case with the manufactureof the recording medium 1, except that processing temperatures andlinear preasures in calendering just after application and drying werechanged appropriately so that the 20-degree specular glosss were 18%,22%, 42% and 47%, respectively.

<<Preparation of Inks>>

[Preparation of Color Ink Set 1]

(Preparation of Pigment Dispersion)

<Preparation of Yellow Pigment Dispersion 1>

Anthranilic acid (1.5 g) was added to 10 g of a hydrochloric acidsolution (6 mol/L), subsequently cooled to 5° C., 1.8 g of sodiumnitrite was added, and stirred. Powder of C.I. Pigment Yellow-74 (5 g)was added thereto, a liquid temperature was raised to 80° C. withstirring, heating was continued until production of nitrogen gasstopped, and cooled. Then, acetone was added, and a yellow dispersion 1was yielded by filtrating pigment particles, washing with ion-exchangewater, subsequently adding ion-exchange water, performing respectiveoperations of ion exchange, ultrafiltration and centrifugation andadjusting with ion-exchange water such that a pigment content was 20% bymass.

<Preparation of Magenta Pigment Dispersion 1>

Anthranilic acid (1.5 g) was added to 10 g of a hydrochloric acidsolution (6 mol/L), subsequently cooled to 5° C., 1.8 g of sodiumnitrite was added, and stirred. Powder of C.I. Pigment Red 122 (5 g) wasadded thereto, a liquid temperature was raised to 80° C. with stirring,heating was continued until production of nitrogen gas stopped, andcooled. Then, acetone was added, and a magenta dispersion 1 was yieldedby filtrating pigment particles, washing with ion-exchange water,subsequently adding ion-exchange water, performing respective operationsof ion exchange, ultrafiltration and centrifugation and adjusting withion-exchange water such that a pigment content was 25% by mass.

<Preparation of Cyan Pigment Dispersion 1>

Anthranilic acid (1.5 g) was added to 10 g of a hydrochloric acidsolution (6 mol/L), subsequently cooled to 5° C., 1.8 g of sodiumnitrite was added, and stirred. Powder of C.I. Pigment Blue 15:3 (5 g)was added thereto, a liquid temperature was raised to 80° C. withstirring, heating was continued until production of nitrogen gasstopped, and cooled. Then, acetone was added, and a cyan dispersion 1was yielded by filtrating pigment particles, washing with ion-exchangewater, subsequently adding ion-exchange water, performing respectiveoperations of ion exchange, ultrafiltration and centrifugation andadjusting with ion-exchange water such that a pigment content was 25% bymass.

<Preparation of Black Pigment Dispersion 1>

Anthranilic acid (1.5 g) was added to 10 g of a hydrochloric acidsolution (6 mol/L), subsequently cooled to 5° C., 1.8 g of sodiumnitrite was added, and stirred. Powder of Carbon black (5 g) was addedthereto, a liquid temperature was raised to 80° C. with stirring,heating was continued until production of nitrogen gas stopped, andcooled. Then, acetone was added, and a black dispersion 1 was yielded byfiltrating pigment particles, washing with ion-exchange water,subsequently adding ion-exchange water, performing respective operationsof ion exchange, ultrafiltration and centrifugation and adjusting withion-exchange water such that a pigment content was 20% by mass.

<Preparation of Blue Pigment Dispersion 1>

Anthranilic acid (1.5 g) was added to 10 g of a hydrochloric acidsolution (6 mol/L), subsequently cooled to 5° C., 1.8 g of sodiumnitrite was added, and stirred. Powder of C.I. Pigment Violet 23 (5 g)was added thereto, a liquid temperature was raised to 80° C. withstirring, heating was continued until production of nitrogen gasstopped, and cooled. Then, acetone was added, and a blue dispersion 1was yielded by filtrating pigment particles, washing with ion-exchangewater, subsequently adding ion-exchange water, performing respectiveoperations of ion exchange, ultrafiltration and centrifugation andadjusting with ion-exchange water such that a pigment content was 20% bymass.

<Preparation of Red Pigment Dispersion 1>

Anthranilic acid (1.5 g) was added to 10 g of a hydrochloric acidsolution (6 mol/L), subsequently cooled to 5° C., 1.8 g of sodiumnitrite was added, and stirred. Powder of C.I. Pigment Red 177 (5 g) wasadded thereto, a liquid temperature was raised to 80° C. with stirring,heating was continued until production of nitrogen gas stopped, andcooled. Then, acetone was added, and a red dispersion 1 was yielded byfiltrating pigment particles, washing with ion-exchange water,subsequently adding ion-exchange water, performing respective operationsof ion exchange, ultrafiltration and centrifugation and adjusting withion-exchange water such that a pigment content was 25% by mass.

[Preparation of Color Ink Set]

Using the respective pigment dispersions prepared above, a color ink set1 composed of a yellow ink 1, a magenta ink 1, a cyan ink 1 and a blackink 1 was prepared. <PREPARATION OF YELLOW INK 1> Yellow pigmentdispersion 1 15% by mass Ethyleneglycol 4% by mass Glycerin 3.75% bymass 2-Pyrrolidone 5% by mass Surfactant (Surfynol 465 supplied fromNisshin the following required Chemical Industry Co., Ltd.) quantityIon-exchange water residual quantity

The surfactant was added such that the surface tension was 38 mN/m and aquantity was adjusted with ion-exchange water such that a total quantitywas 100% by mass. A yellow ink 1 was prepared by mixing the abovecompositions, stirring and filtrating with a 1 μm filter. A meanparticle size of pigments in the ink was 131 nm. <PREPARATION OF MAGENTAINK 1> Magenta pigment dispersion 1 15% by mass Glycerin 8% by massDiethyleneglycol 1.75% by mass 2-Pyrrolidone 3% by mass Surfactant(Surfynol 465 supplied from Nisshin the following required ChemicalIndustry Co., Ltd.) quantity Ion-exchange water residual quantity

The surfactant was added such that the surface tension was 38 mN/m and aquantity was adjusted with ion-exchange water such that a total quantitywas 100% by mass. A magenta ink 1 was prepared by mixing the abovecompositions, stirring and filtrating with a 1 μm filter. A meanparticle size of pigments in the ink was 129 nm. <PREPARATION OF CYANINK 1> Cyan pigment dispersion 1 10% by mass Ethyleneglycol 8% by massDiethyleneglycol 4% by mass Glycerin 5% by mass 2-Pyrrolidone 2% by massSurfactant (Surfynol 465 supplied from Nisshin the following requiredChemical Industry Co., Ltd.) quantity Ion-exchange water residualquantity

The surfactant was added such that the surface tension was 38 mN/m and aquantity was adjusted with ion-exchange water such that a total quantitywas 100% by mass. A cyan ink 1 was prepared by mixing the abovecompositions, stirring and filtrating with a 1 μm filter. A meanparticle size of pigments in the ink was 104 nm. <PREPARATION OF BLACKINK 1> Black pigment dispersion 1 10% by mass Glycerin 5% by massEthyleneglycol 7% by mass 2-Pyrrolidone 2% by mass Surfactant (Surfynol465 supplied from Nisshin the following required Chemical Industry Co.,Ltd.) quantity Ion-exchange water residual quantity

The surfactant was added such that the surface tension was 38 mN/m and aquantity was adjusted with ion-exchange water such that a total quantitywas 100% by mass. A black ink 1 was prepared by mixing the abovecompositions, stirring and filtrating with a 1 μm filter. A meanparticle size of pigments in the ink was 98 nm. <PREPARATION OF BLUE INK1> Blue pigment dispersion 1 15% by mass Glycerin 8% by massDiethyleneglycol 1.75% by mass 2-Pyrrolidone 3% by mass Surfactant(Surfynol 465 supplied from Nisshin the following required ChemicalIndustry Co., Ltd.) quantity Ion-exchange water residual quantity

The surfactant was added such that the surface tension was 38 mN/m and aquantity was adjusted with ion-exchange water such that a total quantitywas 100% by mass. A blue ink 1 was prepared by mixing the abovecompositions, stirring and filtrating with a 1 μm filter. A meanparticle size of pigments in the ink was 129 nm. <PREPARATION OF RED INK1> Red pigment dispersion 1   15% by mass Glycerin   8% by massDiethyleneglycol 1.75% by mass 2-Pyrrolidone   3% by mass Surfactant(Surfynol 465 supplied from the following required Nisshin ChemicalIndustry Co., Ltd.) quantity Ion-exchange water residual quantity

The surfactant was added such that the surface tension was 38 mN/m and aquantity was adjusted with ion-exchange water such that a total quantitywas 100% by mass. A red ink 1 was prepared by mixing the abovecompositions, stirring and filtrating with a 1 μm filter. A meanparticle size of pigments in the ink was 123 nm.

[Preparation of Color Ink Set 2]

A color ink set 2 was made up of basic inks (yellow ink 1, magenta ink1, cyan ink 1 and black ink 1) as is the case with the above preparationof the ink set 1 except the blue ink 1 and the red ink 1 which werespecial color inks.

[Preparation of Color Ink Set 3]

<Preparation of Green Pigment Dispersion 1>

Anthranilic acid (1.5 g) was added to 10 g of a hydrochloric acidsolution (6 mol/L), subsequently cooled to 5° C., 1.8 g of sodiumnitrite was added, and stirred. Powder of C.I. Pigment Green 7 (5 g) wasadded thereto, a liquid temperature was raised to 80° C. with stirring,heating was continued until production of nitrogen gas stopped, andcooled. Then, acetone was added, and a green dispersion 1 was yielded byfiltrating pigment particles, washing with ion-exchange water,subsequently adding ion-exchange water, performing respective operationsof ion exchange, ultrafiltration and centrifugation and adjusting withion-exchange water such that a pigment content was 25% by mass.<PREPARATION OF GREEN INK 1> Green pigment dispersion 1   15% by massGlycerin   8% by mass Diethyleneglycol 1.75% by mass 2-Pyrrolidone   3%by mass Surfactant (Surfynol 465 supplied from the following requiredNisshin Chemical Industry Co., Ltd.) quantity Ion-exchange waterresidual quantity

The surfactant was added such that the surface tension was 38 mN/m and aquantity was adjusted with ion-exchange water such that a total quantitywas 100% by mass. A green ink 1 was prepared by mixing the abovecompositions, stirring and filtrating with a 1 μm filter. A meanparticle size of pigments in the ink was 104 nm.

[Preparation of Color Ink Set 3]

A color ink set 3 was made up as is the case the above preparation ofthe ink set 1 except using of the green ink 1 instead of the blue ink 1and the red ink 1 which were special color inks.

[Preparation of Ink Set 4]

(Preparation of Pigment Dispersion) <PREPARATION OF YELLOW PIGMENTDISPERSION 2> C.I. Pigment Yellow-74 20% by mass Polymeric dispersantSA-1 10% by mass (as a solid content) Glycerin 15% by mass Ion-exchangewater 55% by mass

The above additives were mixed and dispersed using a horizontal typebead mill (System Zeta mill supplied from Ashizawa Finetech Ltd.) inwhich zirconia beads of 0.3 mm were filled at a volume rate of 60% toyield a yellow pigment dispersion 2. A mean particle size of theobtained yellow pigments was 112 nm. <PREPARATION OF MAGENTA PIGMENTDISPERSION 2> C.I. Pigment Red 122 25% by mass Polymeric dispersant SA-216% by mass (as a solid content) Glycerin 15% by mass Ion-exchange water44% by mass

The above additives were mixed and dispersed using a horizontal typebead mill (System Zeta mill supplied from Ashizawa Finetech Ltd.) inwhich zirconia beads of 0.3 mm were filled at a volume rate of 60% toyield a magenta pigment dispersion 2. A mean particle size of theobtained magenta pigments was 105 nm. <PREPARATION OF CYAN PIGMENTDISPERSION 2> C.I. Pigment Blue 15:3 25% by mass Polymeric dispersantSA-1 13% by mass (as a solid content) Diethyleneglycol 10% by massIon-exchange water 52% by mass

The above additives were mixed and dispersed using a horizontal typebead mill (System Zeta mill supplied from Ashizawa Finetech Ltd.) inwhich zirconia beads of 0.3 mm were filled at a volume rate of 60% toyield a cyan pigment dispersion 2. A mean particle size of the obtainedcyan pigments was 87 nm. <PREPARATION OF BLACK PIGMENT DISPERSION 2>Carbon black 20% by mass Polymeric dispersant SA-1  9% by mass (as asolid content) Glycerin 10% by mass Ion-exchange water 61% by mass

The above additives were mixed and dispersed using a horizontal typebead mill (System Zeta mill supplied from Ashizawa Finetech Ltd.) inwhich zirconia beads of 0.3 mm were filled at a volume rate of 60% toyield a black pigment dispersion 2. A mean particle size of the obtainedblack pigments was 75 nm <PREPARATION OF BLUE PIGMENT DISPERSION 2> C.I.Pigment Violet 23 25% by mass Polymeric dispersant SA-1 13% by mass (asa solid content) Ethyleneglycol 10% by mass Ion-exchange water 52% bymass

The above additives were mixed and dispersed using a horizontal typebead mill (System Zeta mill supplied from Ashizawa Finetech Ltd.) inwhich zirconia beads of 0.3 mm were filled at a volume rate of 60% toyield a blue pigment dispersion 2. A mean particle size of the obtainedcyan pigments was 107 nm <PREPARATION OF RED PIGMENT DISPERSION 2> C.I.Pigment Red 177 20% by mass Polymeric dispersant SA-2 16% by mass (as asolid content) Glycerin 15% by mass Ion-exchange water 49% by mass

The above additives were mixed and dispersed using a horizontal typebead mill (System Zeta mill supplied from Ashizawa Finetech Ltd.) inwhich zirconia beads of 0.3 mm were filled at a volume rate of 60% toyield a red pigment dispersion 2. A mean particle size of the obtainedmagenta pigments was 98 nm.

Each polymeric dispersant used for each of the above-described pigmentdisperions was prepared according to the following method.

[Preparation of Polymeric Dispersant]

<Preparation of Polymeric Dispersant SA-1>

A 3 L four-necked flask was equipped with a three one motor, athermometer, a nitrogen charging tube and a dropping funnel with adrying tube. With running dried nitrogen gas, tetrahydrofuran (780.0 g)and p-xylene (3.6 g) were charged into this. With stirring,tetrabutylammonium m-benzoate (solution at 1 mol/L, 3.2 ml) was added,and further 1,1-bis(trimethylsiloxy)-2-methylpropene (144.0 g) wasadded.

Next, tetrabutylammonium m-benzoate (solution at 1 mol/L, 3.2 ml) wasdripped from the dropping funnel over 130 min with stirring. Afterdripping, a mixture of benzyl methacrylate (272.6 g) and trimethylsilylmethacrylate (489.8 g) was dripped from the dropping funnel over 40 minwith stirring. After stirring for 30 min, benzyl methacrylate (545.4 g)was dripped from the dropping funnel over 30 min with stirring.

After stirring as it was for 240 min, absolute methanol (216 g) wasadded and stirred. The dropping funnel was changed to Liebig condenser,an entire vessel was heated, and a fraction of distillate at a boilingpoint of 55° C. or below was eliminated. Distillation was furthercontinued, at the time point when the boiling point was 76° C.,2-propanol (900 g) was added, and heating and distillation were furthercontinued. Heating was continued until a solvent at a total amount of1,440 g was run out to yield a solution 1 of an aimed block copolymer(BzMA//BzMA/MAA=5//2.5/5). A part was dried, a molecular weight and anacid value were measured, and they were 1,500 and 70, respectively.

This solution 1 was neutralized by adding N,N-dimethylethanolamine toyield an aimed polymeric dispersant SA-1.

[Preparation of Polymeric Dispersant SA-2]

A polymeric dispersant SA-2 was prepared as was the case with thepreparation of the polymeric dispersant SA-1, except that neutralizationwas performed using potassium hydroxide in place ofN,N-dimethylethanolamine.

(Preparation of Pigment Ink Set)

A color ink set 4 was prepared as was the case with the abovepreparation of the ink set 1, except that the yellow pigment dispersion2, the magenta pigment dispersion 2, the cyan pigment dispersion 2, theblack pigment dispersion 2, the blue pigment dispersion 2 and the redpigment dispersion 2 which were prepared above were used instead of theyellow pigment dispersion 1, the magenta pigment dispersion 1, the cyanpigment dispersion 1, the black pigment dispersion 1, the blue pigmentdispersion 1 and the red pigment dispersion 1.

[Preparation of Ink Set 5]

An ink set 5 was prepared as was the case with the above preparation ofthe ink set 3, except that the cyan ink 2 was changed to the cyan ink 3prepared according to the following procedure.

(Preparation of Pigment Dispersion) <PREPARATION OF CYAN PIGMENTDISPERSION 3> C.I. Pigment Blue 15:3   26 g SA-3 solution   28 g Aqueoussolution of potassium 13.6 g hydroxide at 1 mol/L Methylethylketone   20g Ion-exchange water   30 g

The above additives were mixed and kneaded 20 times using a three rollmill. The obtained paste was added into ion-exchange water (200 g),stirred thoroughly, and subsequently methylethylketone and water weredistilled off using a rotary evaporator such that the solid content was20% to yield a cyan pigment dispersion 2.

The polymeric dispersant SA-3 used for the above-described cyan pigmentdisperion 3 was prepared according to the following method.

[Preparation of Polymeric Dispersant SA-3]

A 1 L four-necked flask was equipped with a three one motor, athermometer, a reflux tube with a nitrogen charging tube and a droppingfunnel. With running dried nitrogen gas, the following monomer mixture 1was charged into this, and a temperature was raised to 65° C.

Next, the following monomer mixture 2 was dripped over 2.5 hours withstirring. Further, a mix solution of azobisdimethylvaleronitrile (0.8 g)and methylethylketone (22 ml) was dripped over 0.5 hours.Azobisdimethylvaleronitrile (0.8 g) was added and further heated andstirred for one hour.

After completion of the reaction, methylethylketone (450 ml) was addedto yield a solution of a polymeric dispersant SA-3 with solid content of50%. A part was dried, a molecular weight and an acid value weremeasured, and they were 15,000 and 55, respectively. (MONOMER MIXTURE 1)Styrene 11.2 g Lauryl methacrylate 12.0 g Polyethyleneglycolmethacrylate (Light  4.0 g Ester 130MA supplied from Kyoeisha ChemicalCo., Ltd.) Styrene macromer (Macromonomer AS-6  4.0 g supplied fromToagosei Co., Ltd.) Acrylic acid  2.8 g Mercaptoethanol  0.4 g

(MONOMER MIXTURE 2) Styrene 100.8 g Lauryl methacrylate 108.0 gHydroxyethyl methacrylate 60.0 g Polyethyleneglycol methacrylate (LightEster 130MA 36.0 g supplied from Kyoeisha Chemical Co., Ltd.) Styrenemacromer (Macromonomer AS-6 supplied from 36.0 g Toagosei Co., Ltd.)Acrylic acid 25.2 g Mercaptoethanol 3.6 g Azobisdimethylvaleronitrile2.4 g Methylethylketone 22 ml

<PREPARATION OF CYAN INK 3> Cyan pigment dispersion 3 10% by mass Ethyleneglycol 8% by mass Diethyleneglycol 6% by mass Glycerin 4% bymass 2-Pyrrolidone 3% by mass Urea 3% by mass Surfactant (Surfynol 465supplied from Nisshin the following required Chemical Industry Co.,Ltd.) quantity Ion-exchange water residual quantity

The surfactant was added such that the surface tension was 38 mN/m and aquantity was adjusted with ion-exchange water such that a total quantitywas 100% by mass. A cyan ink 3 was prepared by mixing the abovecompositions, stirring and filtrating with a 1 μm filter. A meanparticle size of pigments in the ink was 98 nm.

[Preparation of Ink Set 6]

(Preparation of Pigment Dispersion)

A yellow pigment dispersion 3, a magenta pigment dispersion 3, a cyanpigment dispersion 4, a black pigment dispersion 3, a blue pigmentdispersion 3 and a red pigment dispersion 3 were prepared as is the casewith the above preparation of the yellow pigment dispersion 2, themagenta pigment dispersion 2, the cyan pigment dispersion 2, the blackpigment dispersion 2, the blue pigment dispersion 2 and the red pigmentdispersion 2 except that sodium naphthalenesulfonate was used instead ofthe polymeric dispersants SA-1 and SA-2.

(Preparation of Color Ink Set]

A color ink set 6 was prepared as was the case with the abovepreparation of the ink set 1, except that the yellow pigment dispersion3, the magenta pigment dispersion 3, the cyan pigment dispersion 4, theblack pigment dispersion 3, the blue pigment dispersion 3 and the redpigment dispersion 3 which were prepared above were used instead of theyellow pigment dispersion 1, the magenta pigment dispersion 1, the cyanpigment dispersion 1, the black pigment dispersion 1, the blue pigmentdispersion 1 and the red pigment dispersion 1.

[Preparation of Ink Sets 7 to 9]

Ink sets 7 to 9 were prepared as was the case with the above preparationof the ink set 1, except that the surface tension of the respectivecolor inks was made 28 mN/m, 48 mN/m, and 55 mN/m, respectively byappropriately conditioning the addition amounts of the polymericdispersants used for the preparation of the respective pigmentdispersions and the surfactant used for the preparation of the ink.

[Preparation of Ink Set 10]

An ink set 10 was prepared as was the case with the above preparation ofthe ink set 1, except that 5% by mass of ethylene urea was added to eachcolor ink.

<<Measurement of Property Values of Recording Media and Inks>>

[Recording Medium: Measurement of Transferred Amount]

The transferred amount at 0.04 seconds of absorption time by Bristowmethod was measured in each recording medium made above according to thefollowing method.

As the method of measuring the transferred amount, after leaving therecording medium under an atmosphere at 25° C. and 50% RH for 12 hoursor more, the measurement was performed using a Bristow testing machineII type (press mode) which was a liquid dynamic absorbability testingmachine supplied from Kumagai Rikikogyo Co., Ltd. The aqueous solutionof 2% C.I. acid red 52 was used for the measurement and the transferredamount can be obtained by measuring an area stained with magenta on therecording medium after 0.04 seconds of absorption time.

[Calculation of Void Rate]

The void rate of each recording medium made above was calculated bycalculation from a void capacity obtained from Bristow method and atotal volume of the micro-porous layer obtained from a dried filmthickness.

[Ink Set: Measurement of Surface Tension]

For the surface tension of the ink which composes the ink set, a surfacetension value (mN/m) at an ink temperature of 25° C. was measured by aplatinum plate method using a tensiometer (CBVP-Z supplied from KyowaInterface Science Co., Ltd.)

[20-Degree Specular Gloss]

The 20-degree specular gloss on the side of an ink absorbing layerapplication surface of each recording medium was measured by using thedigital variable angle glossmeter (supplied from Suga Test InstrumentsCo., Ltd.) according to JIS-Z-8741.

<<Printing Methods>>

[Printing Method 1]

Each ink set prepared above was set in an on-demand type inkjet printerwith a maximum recording density main scanning 1200× sub scanning 1200dpi having thermal type heads which arrange two rows with 1 mm distanceof nozzle rows and enable to effectively form 256 dots with 1200 dpipitch by arraying the nozzles in two rows with a shift of 21.2 μm in asub scanning direction, where a nozzle pore size was 15 μm, a drivingfrequency was 20 kHz, an amount of an ink droplet was 3 pl, a dot sizeafter jetted on the recording medium was 35 μm, a nozzle number in onerow was 128 and a nozzle pitch was 42.3 μm and one-pass printing wasperformed without using the thinning-out pattern. Here, dpi referred torepresents a dot number per 2.54 cm. The image data were extracted bythe method described in paragraph numbers [0038] to [0059] ofJP-Tokukaihei-2000-32284A.

Relationship between the image data and ink amount to be used in thiscase is shown in FIG. 24, which takes a blue hue as an example.

In FIG. 24, the adhesive amounts of the cyan ink A and the magenta ink Bincrease as the tone level rises, whereas at the gradation level 7 orhigher, the blue ink C is used and the magenta ink B is reduced. Thecyan ink A is not reduced, but an increment amount thereof is decreasedcompared to the case where the blue ink C is not used. At the gradationlevel 16, solid of the blue ink C is adhered, and the use amount oftotal inks is 20.5 ml/m². It is for creating visually preferable colorsthat the cyan ink A and some magenta ink B are used even on the solid ofblue ink C.

[Printing Method 2]

Each ink set prepared above was set in an on-demand type inkjet printerwith a maximum recording density main scanning 1200× sub scanning 1200dpi having thermal type heads which arrange two rows with 1 mm distanceof nozzle rows and enable to effectively form 256 dots with 1200 dpipitch by arraying nozzles in two rows with a shift of 21.2 μm in a subscanning direction where a nozzle pore size was 15 μm, a drivingfrequency was 20 kHz, an amount of an ink droplet was 3 pl, a dot sizeafter jetted on the recording medium was 35 μm, a nozzle number in onerow was 128 and a nozzle pitch was 42.3 μm, and the formation ofthinned-out image was performed by four-pass printing using the regularthinning-out pattern at a printing acceptable rate of 25%. The masksused are shown in FIG. 23. The method for extracting image data wasalong with the printing method 1.

[Printing Method 3]

Each ink set prepared above was set in an on-demand type inkjet printerwith a maximum recording density main scanning 1200× sub scanning 1200dpi having thermal type heads which arrange two rows with 1 mm distanceof nozzle rows and enable to effectively form 256 dots with 1200 dpipitch by arraying nozzles in two rows with a shift of 21.2 μm in a subscanning direction where a nozzle pore size was 15 μm, a drivingfrequency was 20 kHz, an amount of an ink droplet was 3 pl, a dot sizeafter jetted on the recording medium was 35 μm, a nozzle number in onerow was 128 and a nozzle pitch was 42.3 μm, and the formation ofthinned-out image was performed by four-pass printing using thethinning-out pattern without regularity at a printing acceptable rate of25%. The masks used are shown in FIG. 18.

[Printing Method 4]

A printing method 4 was performed as was the case with the aboveprinting method 3, except that effectively heads of 2400 dpi were madeto make printing resolution of the maximum recording density mainscanning 2400× sub scanning 2400 dpi by appropriately changing thenozzle pore size to make the ink droplet (about 0.75 pl) such that thedot size after jetted on the recording medium was 15 μm, making thenozzle pitch of one row 21.2 μm and making the shift between the tworows 10.6 μm. The method for extracting image data was along with theprinting method 1.

[Printing Method 5]

A printing method 5 was performed as was the case with the aboveprinting method 3, except that the nozzle pore size was appropriatelychanged such that the ink droplet amount was about 5 pl whichcorresponded to the dot size of 40 μm after jetted on the recordingmedium. The image data were precedently conditioned such that an inkadhesive amounts on the medium were nearly identical to those in theprinting method 3. The method for extracting image data was along withthe printing method 1.

[Printing Method 6]

A printing method 6 was performed as was the case with the aboveprinting method 3, except that the nozzle pore size was appropriatelychanged such that the ink droplet amount was about 14 pl whichcorresponded to the dot size of 60 μm after jetted on the recordingmedium. The image data were precedently conditioned such that an inkadhesive amounts on the medium were nearly identical to those in theprinting method 3. The method for extracting image data was along withthe printing method 1.

[Printing Method 7]

A printing method 7 was performed as was the case with the aboveprinting method 3, except that the heads were changed to the heads wherethe nozzle pitch is 15 μm and 256 nozzles were arranged in one row tomake the maximum recording density main scanning 850× sub scanning 1690dpi. The sub scanning resolution corresponded to the head nozzle pitch,and the main scanning resolution was changed depending on this such thatthe ink adhesive amounts on the medium were nearly identical to those inthe printing method 3. The method for extracting image data was alongwith the printing method 1.

[Printing Method 8]

A printing method 8 was performed as was the case with the aboveprinting method 3, except changing to the maximum recording density mainscanning 1570× sub scanning 920 dpi by changing to the nozzle headswhere the nozzle groups where 256 nozzles were arranged in one row witha nozzle pitch of 55 μm were separated by 2 cm, two rows for each colorwere arranged with a shift of 27.5 μm in the subscanning direction, and512 nozzles per color were arranged. In this case, the nozzle pitch is55 μm. The sub scanning resolution corresponded to the dot pitch on themedium, and the main scanning resolution was changed depending on thissuch that the ink adhesive amounts on the medium were nearly identicalto those in the printing method 3. The method for extracting image datawas along with the printing method 1.

[Printing Method 9]

A printing method 9 was performed as was the case with the aboveprinting method 3, except changing the printing acceptable rate to arepeat of four types of 40%, 40%, 10% and 10% (thus the printingacceptable rate was 40%). The method for extracting image data was alongwith the printing method 1.

[Printing Method 10]

A printing method 10 was performed as was the case with the aboveprinting method 3, except changing to the maximum recording density mainscanning 1200× sub scanning 1200 dpi by changing to the nozzle headswhere the nozzle groups where 256 nozzles were arranged in one row witha nozzle pitch of 42.3 μm were separated by 2 cm, two rows for eachcolor were arranged with a shift of 21.2 μm in the subscanningdirection, and 512 nozzles per color were arranged. In this case, thenozzle pitch is 42.3 μm. The method for extracting image data was alongwith the printing method 1.

<<Formation of Inkjet Recording Image>>

Solid image printing of the respective colors of yellow, magenta, cyan,green, red, blue and black was performed by combining the above printingmethod, the recording medium and the ink set made above as described inTables 1, 2 and 3 to make the images 1 to 42, and the obtained imageswere evaluated as follows. TABLE 1 Recording medium Inorganic Printingmode particle Printing Mean Hardener 20- Nozzle Dot acceptable particlepresence Void degree Image pitch size rate size or rate specular No. No.(μm) (μm) (%) No. Support Type (μm) *2 absence (%) gloss (%) 1 1 21.2 35— 1 Water- Silica 35 16 Presence 40 24 absorbable 2 2 21.2 35 25 1Water- Silica 35 16 Presence 40 24 absorbable 3 3 21.2 35 25 1 Water-Silica 35 16 Presence 40 24 absorbable 4 3 21.2 35 25 1 Water- Silica 3516 Presence 40 24 absorbable 5 3 21.2 35 25 1 Water- Silica 35 16Presence 40 24 absorbable 6 3 21.2 35 25 2 Non water- Silica 35 8Presence 40 22 absorbable 7 3 21.2 35 25 3 Non water- Silica 35 16Presence 40 22 absorbable 8 3 21.2 35 25 4 Water- Silica 35 11 Presence35 24 absorbable 9 3 21.2 35 25 4 Water- Silica 35 11 Presence 35 24absorbable 10 3 21.2 35 25 5 Water- Alumina 30 22 Presence 55 32absorbable 11 3 21.2 35 25 6 Water- Silica 15 16 Presence 48 27absorbable 12 3 21.2 35 25 6 Water- Silica 15 16 Presence 48 27absorbable 13 3 21.2 35 25 7 Water- Silica 80 16 Presence 61 21absorbable 14 3 21.2 35 25 7 Water- Silica 80 16 Presence 61 21absorbable 15 3 21.2 35 25 8 Water- Silica 120 16 Presence 68 16absorbable 16 3 21.2 35 25 9 Water- Silica 35 16 Absence 40 21absorbable 17 3 21.2 35 25 9 Water- Silica 35 16 Absence 40 21absorbable 18 3 21.2 35 25 10 Water- Silica 35 4 Presence 25 25absorbable 19 3 21.2 35 25 11 Water- Silica 35 28 Presence 75 22absorbable 20 3 21.2 35 25 12 Water- Silica 35 16 Presence 52 18absorbable 21 3 21.2 35 25 13 Water- Silica 35 16 Presence 42 22absorbable*1: 40, 40, 10 and 10 (equivalent to 40%)*2: Transported amount (ml/m²)

TABLE 2 Recording medium Inorganic Printing mode particles Printing MeanHardener Nozzle Dot acceptable particle presence Void 20-degree Imagepitch size rate size or rate specular No. No. (μm) (μm) (%) No. SupportType (μm) *2 absence (%) gloss (%) 22 3 21.2 35 25 13 Water- Silica 3516 Presence 42 22 absorbable 23 3 21.2 35 25 14 Water- Silica 35 12Presence 30 42 absorbable 24 3 21.2 35 25 14 Water- Silica 35 12Presence 30 42 absorbable 25 3 21.2 35 25 15 Water- Silica 35 8 Presence21 47 absorbable 26 3 21.2 35 25 1 Water- Silica 35 16 Presence 40 24absorbable 27 3 21.2 35 25 1 Water- Silica 35 16 Presence 40 24absorbable 28 3 21.2 35 25 1 Water- Silica 35 16 Presence 40 24absorbable 29 3 21.2 35 25 1 Water- Silica 35 16 Presence 40 24absorbable 30 3 21.2 35 25 1 Water- Silica 35 16 Presence 40 24absorbable 31 3 21.2 35 25 1 Water- Silica 35 16 Presence 40 24absorbable 32 3 21.2 35 25 5 Water- Alumina 30 22 Presence 55 32absorbable 33 4 21.2 15 25 1 Water- Silica 35 16 Presence 40 24absorbable 34 4 21.2 15 25 1 Water- Silica 35 16 Presence 40 24absorbable 35 5 21.2 40 25 1 Water- Silica 35 16 Presence 40 24absorbable 36 6 21.2 60 25 1 Water- Silica 35 16 Presence 40 24absorbable 37 7 15.0 35 25 1 Water- Silica 35 16 Presence 40 24absorbable 38 7 15.0 35 25 1 Water- Silica 35 16 Presence 40 24absorbable 39 8 55.0 35 25 1 Water- Silica 35 16 Presence 40 24absorbable 40 9 21.2 35 *1 1 Water- Silica 35 16 Presence 40 24absorbable 41 10 42.3 35 25 1 Water- Silica 35 16 Presence 40 24absorbable 42 10 42.3 35 25 1 Water- Silica 35 16 Presence 40 24absorbable*1: 40, 40, 10 and 10 (equivalent to 40%)*2: Transported amount (ml/m²)

TABLE 3 Coloring ink set Urea Printing Recording presence Imge modemedium Pigment or Surface No. No. No. No. dispersant absence tension *3Remarks 1 1 1 1 — Absence 38 Comparative example 2 2 1 1 — Absence 38Comparative example 3 3 1 2 — Absence 38 Comparative example 4 3 1 1 —Absence 38 Present invention 5 3 1 3 — Absence 38 Present invention 6 32 1 — Absence 38 Comparative example 7 3 3 1 — Absence 38 Presentinvention 8 3 4 1 — Absence 38 Present invention 9 3 4 4 SA-1 and 2Absence 38 Present invention 10 3 5 1 — Absence 38 Present invention 113 6 1 — Absence 38 Present invention 12 3 6 4 SA-1 and 2 Absence 38Present invention 13 3 7 1 — Absence 38 Present invention 14 3 7 4 SA-1and 2 Absence 38 Present invention 15 3 8 1 — Absence 38 Comparativeexample 16 3 9 1 — Absence 38 Present invention 17 3 9 4 SA-1 and 2Absence 38 Present invention 18 3 10 1 — Absence 38 Comparative example19 3 11 1 — Absence 38 Present invention 20 3 12 1 — Absence 38Comparative example 21 3 13 1 — Absence 38 Present invention 22 3 13 4SA-1 and 2 Absence 38 Present invention 23 3 14 1 — Absence 38 Presentinvention 24 3 14 4 SA-1 and 2 Absence 38 Present invention 25 3 15 1 —Absence 38 Comparative example 26 3 1 4 SA-1 and 2 Absence 38 Presentinvention 27 3 1 5 SA-1 to 3 Absence 38 Present invention 28 3 1 6 *4Absence 38 Present invention 29 3 1 7 SA-1 and 2 Absence 28 Presentinvention 30 3 1 8 SA-1 and 2 Absence 48 Present invention 31 3 1 9 SA-1and 2 Absence 55 Present invention 32 3 5 10 SA-1 and 2 Presence 37Present invention 33 4 1 1 — Absence 38 Present invention 34 4 1 4 SA-1and 2 Absence 38 Present invention 35 5 1 1 — Absence 38 Presentinvention 36 6 1 1 — Absence 38 Comparative example 37 7 1 1 — Absence38 Present invention 38 7 1 4 SA-1 and 2 Absence 38 Present invention 398 1 1 — Absence 38 Comparative example 40 9 1 1 — Absence 38 Presentinvention 41 10 1 1 — Absence 38 Present invention 42 10 1 4 SA-1 and 2Absence 38 Present invention*3: mN/m*4: sodium naphthalenesulfonate<<Evaluation of Inkjet Recording Image>>[Evaluation of Gloss Difference]

Images of High Definition Color Digital Standard Image Data “N5 Bicycle”(published in December, 1995) published by Japan Standards Associationobtained by combining the above (printing method, recording medium andinks) were visually observed, and the image quality was evaluatedaccording to the following criteria.

-   -   A: No difference is felt between the gloss of a clock section        with high image density and a color chart section and the gross        of a peripheral white background section, and the clock and the        color chart are looked evenly without standing out in bold        relief from the periphery.    -   B: Some difference is felt between the gloss of the clock        section with high image density and the color chart section and        the gross of the peripheral white background section, but the        clock and the color chart are looked evenly without standing out        in bold relief from the periphery.    -   C: Difference is felt between glosses of the clock section with        high image density and the color chart section and the gross of        the peripheral white background section, and further the clock        and the color chart somewhat stand out in bold relief, but        practically no problem.    -   D: Large gloss difference is felt between the gloss of the clock        section with high image density and the color chart section and        the gloss of the peripheral white background section, and        further the clock and the color chart stand out in bold relief        from the periphery.        [Evaluation of Image Quality]

Images of High Definition Color Digital Standard Image Data “N5 Bicycle”(published in December, 1995) published by Japan Standards Associationobtained by combining the above (printing method, recording medium andinks) were visually observed, and the image quality was evaluatedaccording to the following criteria.

-   -   A: No occurrence of color turbidity and an image with extremely        high definition is obtained.    -   B: Occurrence of slight color turbidity and an image with high        definition is obtained.    -   C: Occurrence of rather turbid color and an image with rather        less distinction, but practically no problem.    -   D: Obvious color turbidity is observed and an image lacks        distinction.        [Evaluation of Depth Feeling]

Images of High Definition Color Digital Standard Image Data “N2Cafeteria” (published in December, 1995) published by Japan StandardsAssociation obtained by combining the above (printing method, recordingmedium and inks) were visually observed, and depth feeling was evaluatedaccording to the following criteria.

-   -   A: An image from which deep depth feeling is felt and which        comes near a silver salt photographic image.    -   B: An image from which depth feeling is felt and which slightly        comes near the silver salt photographic image.    -   C: An image which slightly lacks the depth feeling but is in the        practically acceptable range.    -   D: An image which obviously lacks the depth feeling and is off        from practical use.        [Evaluation of Scratch/Abrasion Resistance]

For the cyan solid image made above, back and forth abrasion wasperformed 10 times on the surface with an office eraser (MONO suppliedfrom Tombow Pencil Co., Ltd.), and the presence or absence of occurrenceof stain on the printed portion was visually determined.

-   -   A: No stain on the printed portion is observed    -   B: Slight stain on the printed portion is observed    -   C: Stain on the printed portion is clearly observed but no        problem in practical use    -   D: Density reduction is clearly observed on the printed portion

The results obtained above are shown in Table 4. TABLE 4 Result ofevaluation Printing Recording Ink Image Scratch/ Image mode medium setBronzing quality abrasion No. No. No. No. resistance Glossiness(definition) resistance Remarks 1 1 1 1 D D D D Comparative example 2 21 1 D D D D Comparative example 3 3 1 2 C B C D Comparative example 4 31 1 B B B C Present invention 5 3 1 3 C B B C Present invention 6 3 2 1C D C D Comparative example 7 3 3 1 C C B C Present invention 8 3 4 1 CC C C Present invention 9 3 4 4 B B B B Present invention 10 3 5 1 A B BC Present invention 11 3 6 1 B C B C Present invention 12 3 6 4 B B B BPresent invention 13 3 7 1 C B C C Present invention 14 3 7 4 B B B BPresent invention 15 3 8 1 D D D C Comparative example 16 3 9 1 C B C CPresent invention 17 3 9 4 B B B B Present invention 18 3 10 1 D D C CComparative example 19 3 11 1 B B B C Present invention 20 3 12 1 D B DC Comparative example 21 3 13 1 B B B C Present invention 22 3 13 4 B BB B Present invention 23 3 14 1 B C C C Present invention 24 3 14 4 B CB B Present invention 25 3 15 1 B D C D Comparative example 26 3 1 4 A BA B Present invention 27 3 1 5 A B A B Present invention 28 3 1 6 C C BC Present invention 29 3 1 7 B B B B Present invention 30 3 1 8 B C B BPresent invention 31 3 1 9 B C C B Present invention 32 3 5 10 A A A APresent invention 33 4 1 1 C C B C Present invention 34 4 1 4 B B B BPresent invention 35 5 1 1 B B B C Present invention 36 6 1 1 D B B DComparative example 37 7 1 1 C B C C Present invention 38 7 1 4 B B B BPresent invention 39 8 1 1 D B D C Comparative example 40 9 1 1 C C C CPresent invention 41 10 1 1 C B C C Present invention 42 10 1 4 B B B BPresent invention

As is obvious from the results in Table 4, it is shown that the goodprinting efficiency is obtained, the obtained images are excellent inbronzing resistance, gloss, scratch/abrasion resistance and imageuniformity, and the images at high definition are obtained in the inkjetrecording method comprising the combination of the recording heads, inksand the recording medium defined in the invention compared toComparative Examples.

According to the present embodiment, even when the color image is formedby printing the pigment inks on the inkjet recording medium according tothe thinning-out pattern without regularity, it is possible to providethe inkjet recording method and the inkjet recording apparatus by whichthe image at high definition with bronzing resistance and no colorturbidity where gloss and scratch/abrasion resistance are improved isobtained.

1. An inkjet recording method comprising the step of: forming a colorimage with color inks on the recording medium by while scanning arecording head multiple times on a same recording area of the recordingmedium, forming a thinned-out image according to an thinning-out patternwithout regularity in each scanning, the recording head having aplurality of nozzle sections for jetting the color inks, wherein anozzle pitch of the recording head is from 10 to 50 μm, the color inkscomprise cyan, magenta, yellow and black inks and at least one specialcolor ink, the color inks contain pigments, at least one organic solventwith high boiling point and water, a dot formed by jetting the colorinks from the recording head has a size of 10 to 50 μm on the recordingmedium, the recording medium has a transferred amount at 0.04 seconds ofabsorption time by Bristow method of 10 ml/m² or more, the recordingmedium comprises a micro-porous layer containing inorganic fineparticles having a mean particle size of 15 to 100 nm and a hydrophilicbinder, and a 20-degree specular gloss of the recording medium accordingto JIS-Z-8741 is 20 to 45%.
 2. The method of claim 1, wherein thespecial color ink is at least one ink selected from a group consistingof a red ink, an orange ink, an blue ink, a violet ink and a green ink.3. The method of claim 1, wherein a printing acceptable rate of thethinning-out pattern is from 15 to 35%.
 4. The method of claim 1,wherein a surface tension of the color inks is from 30 to 50 mN/m. 5.The method of claim 1, wherein the pigments of the color inks aredispersed by a polymeric dispersant.
 6. The method of claim 1, whereinthe recording medium comprises an absorbable support, on which themicro-porous layer is provided.
 7. The method of claim 1, wherein thehydrophilic binder is polyvinyl alcohol or a derivative thereof.
 8. Themethod of claim 1, wherein the hydrophilic binder is hardened.
 9. Themethod of claim 1, wherein a void rate of the micro-porous layer is from30 to 70%.
 10. The method of claim 1, wherein the inorganic fineparticles contain silica or alumina.
 11. The method of claim 1, whereinthe in organic fine particle has the mean particle size of 20 to 80 nm.12. The method of claim 1, wherein the color inks contain urea or a ureaderivative.
 13. An inkjet recording apparatus for forming a color imageby jetting color inks on a recording medium, comprising: a recordinghead having a plurality of nozzle sections to jet the color inks, thenozzle sections being arrayed at a pitch of 10 to 50 μm; a scanningsection to make the recording head scan multiple times on one recordingarea of the recording medium; and a control section to allow therecording head to jet the color inks from the plurality of nozzlesections so that a thinned-out image according to a thinning-out patternwithout regularity in each scanning is formed on the recording medium,wherein the color inks comprise cyan, magenta, yellow and black inks andat least one special color ink, the color inks contains pigments, atleast one organic solvent with high boiling point and water, a dotformed by jetting the color inks from the recording head has a size of10 to 50 μm on the recording medium, the recording medium has atransferred amount at 0.04 seconds of absorption time by Bristow methodis 10 ml/m² or more, the recording medium has a micro-porous layercontaining inorganic fine particles having a mean particle size of 15 to100 nm and a hydrophilic binder, and a 20-degree specular gloss of therecording medium according to JIS-Z-8741 is 20 to 45%.
 14. The apparatusof claim 13, wherein the special color ink is at least one ink selectedfrom a group consisting of a red ink, an orange ink, an blue ink, aviolet ink and a green ink.
 15. The apparatus of claim 13, wherein aprinting acceptable rate of the thinning-out pattern is from 15 to 35%.16. The apparatus of claim 13, wherein a surface tension of the colorinks is from 30 to 50 mN/m.
 17. The apparatus of claim 13, wherein thepigments of the color inks are dispersed by a polymeric dispersant. 18.The apparatus of claim 13, wherein the recording medium comprises anabsorbable support, on which the micro-porous layer is provided.
 19. Theapparatus of claim 13, wherein the hydrophilic binder is polyvinylalcohol or a derivative thereof.
 20. The apparatus of claim 13, whereinthe hydrophilic binder is hardened.
 21. The apparatus of claim 13,wherein a void rate of the micro-porous layer is from 30 to 70%.
 22. Theapparatus of claim 13, wherein the inorganic fine particles containsilica or alumina.
 23. The apparatus of claim 13, wherein the inorganicfine particle has the mean particle size of 20 to 80 nm.
 24. Theapparatus of claim 13, wherein the color inks contain urea or a ureaderivative.